Abstract
This article summarises the research findings of papers published in
Introduction
The purpose of this article is to summarise the research findings of papers published in
The journal's initial mission statement invited papers on “labor market research, labor-management relations, collective bargaining (and) wage determination.” Without doubt, researchers have taken up this invitation with enthusiasm. A search through the
Not every paper published in
The remainder of the article is organized around three core themes in research on professional sports labor markets. The section Pay and Performance in
Pay and Performance in JSE
Kahn (2000) emphasized the strengths of sports labor market data to inform research questions surrounding worker pay and performance. In North American sports especially, firm (team) performance, worker (player) productivity, and salary are all observed in precise detail and, even better, are publicly available for free from online sources.
The theory behind pay and performance models has two components. First, players with scarce ability form job matches with teams under imperfect information (Farber, 1999). Rents from scarce ability are shared between players and teams and there are matching frictions. In North American leagues, the limited numbers of teams (e.g., 32 in National Football League (NFL)s, 30 in MLB), together with restrictions on mobility, confer monopsony power on teams. Leeds & Kowalewski (2001) outline how this matching theory can be applied to the NFL.
The second theoretical strand shows how players (via agents) and teams bargain over pay outcomes. Solow and Krautmann (2020a) show a solution to a Nash bargaining model where teams and free-agent players strive to maximize a joint surplus. For the team, the surplus is the excess of player's marginal revenue product over that of the next best alternative player. The player's surplus is the difference between bargained salary and salary obtainable on the free-agent market. If a bargain is successful, the negotiated pay is positively related to salary of replacement player, salary on the free-agent market, and difference in marginal revenue product between player and next best alternative. Although this theoretical solution was designed with MLB free agents in mind, it can be generalized to free agents in any sports league.
The workhorse model for empirical analysis of pay and performance in sports leagues is Mincer (1974) wage equation expressed generically as:
A common theme of papers published in
The salary measures used in papers covering North American sports are fairly straightforward. MLB and NBA salaries are guaranteed, and data can be garnered from various sources. For NHL, Vincent and Eastman (2009) used data from the players’ union (NHLPA) website but recent data showing “cap hit” values can be found on www.spotrac.com. The cap hit comprises base pay plus prorated signing bonus.
NFL salaries are not guaranteed and papers that model NFL pay use the cap values that are the NFL's official measurement of player salary values set against a team's salary cap. Although data sources for North American sports salaries have changed over time, the principle of open access to publicly available sources has not.
When we turn to European soccer leagues, we find that salary data are severely limited. The only publicly available and reliable source of European soccer salary data is from
Lack of actual salary data has led European researchers to use proxy measures for player pay. Prominent proxies are
In contrast, using a cross-sectional sample of players in Norwegian football, Thrane (2019) finds the correlation between
In
Six papers in
Salary models on North American sports typically deploy age or experience but not both due to collinearity. Age of entry into leagues is most often by draft at the early 20s. Player pay typically has a predicted concave shape in a player experience that reflects diminishing marginal productivity due to physical wear and tear and difficulties in recovery from injury. In Brown et al. (2017), for example, veteran baseball pay peaks at eight years of experience, where six years is the qualifying period for free agency, and the sample mean is 10 years. An interesting behavioral question is whether team executives properly recognize the upcoming downturn in productivity for a new baseballfree agent (Solow & Krautmann, 2020b). In soccer, Lucifora and Simmons (2003) and Thrane (2019) find a turning point for actual pay at age of 28 that does conform to industry expectations of peak player productivity. More generally, the correlations between age and, respectively, expected salary and player performance merit greater attention across various sports leagues.
Measuring player performance is at the heart of player salary estimation. For North American sports, research on baseball has moved on from slugging average for hitters and earned run average for pitchers. On base percentage plus slugging average is now widely applied and is an economically significant predictor of pay. For pitchers, Scully (1974) and Bradbury (2007) emphasize the importance of measures that are independent of fielding, which earned run average is not. As such, Bradbury shows that strikeouts have consistently significant effects on pitcher salary over 1986-2004. Bradbury also suggests that a good metric should feature between season consistency, otherwise it is too noisy to be useful. Again, strikeouts serve this purpose better than earned run average for pitchers.
Several papers modeling NBA salaries have used Wins Produced as a superior measure of player productivity over the NBA's own efficiency measure (Simmons & Berri, 2011). In NFL, yards gained appear to be a good metric for skill position players (Berri & Simmons, 2009). New measures have been developed for offensive linemen including pass and run blocking efficiency by Pro Football Focus. Approximate value is an algorithm-generated single metric available on Pro Football Reference for all NFL positions (Gregory-Smith, 2021).
Soccer is a fluid, interactive sport. Even recent papers on soccer salary models have used very basic indicators such as goals and assists (Carrieri et al., 2018), which are heavily loaded in favor of forward and against defensive players. One alternative to these measures would be journalist ratings such as those from
For each sport, it is possible to find a performance metric that predicts salary. The interesting behavioral questions are whether players are paid according to marginal revenue product, whether anomalies occur in pay setting, whether performance expectations are realized in player contracts, and whether the player labor markets in these sports are efficient. On these broader questions, evidence is mixed. For example, Healy (2008) finds that recent season baseball hitter performances predict player pay far better than previous performances, two to three years back. Healy attributes this result to “memory bias” where team executives take note of most recent performances as salient and reject information from earlier periods. But this result could simply mean that previous performance is not relevant to expectations of future performance imbedded in player contracts. Performances three years back were probably with different players, possibly a different team and in a different context, for example, contention for playoffs. The connection between expected and realized performance merits further research (Krautmann, 2017, 2018).
As a further anomaly, Ashworth and Heyndels (2007) find that young German soccer players born soon after a selection cutoff point for year groups are more likely to be selected for training by Bundesliga teams than later-born players, a relative age effect. Yet, later-born players get a salary premium over early-born players. This could be due to selection on ability (the later-born players are better) or peer effects (the younger players learn from peers in training). This highlights a broader area of neglect in the pay–performance literature. Peer effects and productivity spillovers have received little attention. Arcidiacono et al. (2017) are a notable exception delving into play-by-play NBA data to assess productivity spillovers with the interesting result that spillovers affect team production positively but have little impact on individual salary. Further work to assess productivity spillovers and teammate interactions using high-frequency data in other sports is desirable.
Two papers in
Baseball has undergone several small but significant changes since
Some
Link and Yosifov (2012) estimate a similar model to Krautmann and Oppenheimer (2002) but with different sample periods (1984-1989, 1990-1994, 2003-2006). They use the Win Shares measure, essentially a player's contribution to team wins, as an alternative to slugging. Contract length is again treated as endogenous, this time with the number of disability days in past two years as the instrument. Link and Yosifov broadly confirm the findings of Krautmann and Oppenheimer. For the whole sample over 2003-2006, the interaction coefficient is −0.024 and significant. Restricting the sample to players with at least 10 years of service and using Win Shares, returns to performance are reduced by 2% in exchange for one extra contract year. The trade-off between returns to performance and contract length exists even though pay is positively related to both performance and contract length.
In MLB, many players accept contract extensions while in the final year of their existing contract. The contract extension buys out the remaining contract and adds extra years, potentially with a greater annual salary. If a player still with a rookie contract takes this offer, he will necessarily defer entry into free-agent status. The extension guarantees the team control of player services through the contract extension, while a risk-averse player might see an advantage in avoiding the uncertainty of the free-agent market. Krautmann (2018) argues first that a contract extension typically raises a player's annual salary and second, more contentiously, aligns an MLB player's pay with his marginal revenue product.
In Krautmann (2018), a player's marginal revenue product is assessed relative to the value of output of a replacement player using the Wins Above Replacement (WAR) measure as reported in www.baseball-reference.com. The WAR player is an average AAA player who might appear in MLB as a replacement for an injured player. It is important to stress that Krautmann (2018) is estimating
The connection between pay and marginal revenue product is investigated by Solow and Krautmann (2020b). Starting with the notion of long-term contracts as a mechanism for players and teams to share risks, they estimate present values of marginal revenues and future salaries. The estimates reveal a negative surplus, with marginal cost above team marginal benefits for the majority of long-term contracts that they observe. As with Krautmann (2018), the present value estimates are net of pay and productivity contributions of replacement player as captured by WAR. Further work is needed to assess the results of Krautmann (2018) and Solow and Krautmann (2020b) using metrics for the productivity of replacement player other than WAR. More generally, the effects of different contract types on the relationship between pay and marginal revenue product merit further analysis, not just for MLB.
Gregory-Smith (2021) offers an alternative approach for NFL players based on lost cap value to teams from injured players. Gregory-Smith finds that, on average, NFL players have pay equal to marginal revenue product but this conceals heterogeneity. As is well-known, rookie players are subject to monopsony exploitation and receive pay below marginal revenue product. Therefore, Gregory-Smith's results imply that some veterans have pay
Discrimination
The presence of various racial and ethnic groups in sports teams leads naturally to the consideration of possible discrimination. This is broadly defined as unequal treatment of groups of players of similar characteristics, including productivity. Unequal treatment covers pay, hiring, and career length (exit discrimination). Sources of taste-based pay discrimination are employer, customer/fan, and coworker (teammates). Statistical discrimination in pay via stereotyping of particular groups of players is another possibility. Unlike papers on bargaining and contracts, papers are spread widely across North American leagues with five on NFL, four on NBA, and three on NHL. MLB is featured in just two papers and soccer also has two.
Following Becker (1957), taste-based discrimination should not persist in competitive product and labor markets as firms that avoid discrimination should gain a competitive advantage. This forces discriminating firms to either exit their industry or abandon pay discrimination. Goff et al. (2002) draw upon this principle to explain the process of integration of Black players into MLB in the 1940s and 1950s, starting with the famous example of Jackie Robinson. According to Goff et al., a small group of “entrepreneurial” teams led the process of Black player integration that was then followed by all teams. This argument is challenged empirically by Hanssen and Meehan (2009).
Early papers on pay discrimination in
Standard empirical labor economics treatment of pay discrimination offers wage equations estimated separately for groups of players. This is typically followed by an Oaxaca–Blinder decomposition that breaks down the mean pay gap between worker types into endowments (quantities of characteristics) and returns to characteristics. Differences in returns to characteristics indicate pay discrimination, again assuming sufficient productivity measures.
The basic Oaxaca–Blinder approach has not generally been followed in papers published in
The basic Oaxaca–Blinder decomposition is applied to mean pay gaps. But in sports leagues especially, with a skewed distribution of log salary, it is important to investigate pay disparities away from the mean. The Melly (2006) decomposition generalizes the Oaxaca–Blinder procedure to quantile regressions, and this approach has been applied in two papers in
Burnett and Van Scyoc (2015) model pay of linebackers and offensive linemen also over 2001-2009 but with a different sample to Keefer. Using both a Black dummy and quantile treatment effects in quantile regressions, they find no evidence of pay discrimination against Black players. The authors’ rationale for the difference in results from Keefer (2013) is that their sample was based on a later period of entry into the NFL in which awareness of discrimination had increased. This echoes Goff et al. (2002) and presents an intriguing problem for further work. If it is indeed the case that pays discrimination against Black linebackers was present in the 1990s but not later on, then how did discrimination get removed? The numbers of Black and White offensive linemen and linebackers should be sufficient to estimate Melly quantile treatment effects.
Following the seminal work of Szymanski (2000) on discrimination in English football in the 1970s and 1980s, Mongeon (2015) performs a “market test” on NHL. This involves regressing team performance on team (relative) payrolls and shares of ethnic groups on NHL team rosters. Mongeon finds significant coefficients on ethnic group shares in both OLS and IV estimations where team payrolls are endogenous. Of course, this exercise depends on team relative payroll being a good proxy for team quality which Mongeon argues does hold for NHL despite the presence of a hard salary cap.
Instead of using a Black dummy variable, Robst et al. (2011) adopt a continuous measure of skin color derived from skin pigmentation and assessed by software. Applying this measure to NBA salaries, they find an insignificant coefficient on their “skin tone” measure, and this indicates the absence of pay discrimination in this league.
The only paper in
Groothuis and Hill (2018) model career durations using hazard functions estimated overall NBA players between 1990 and 2013. Foreign-born players who did not play college basketball in United States have shorter careers than US-born players. This could reflect exit discrimination. However, foreign-born players who did play college basketball in United States do not have shorter careers than US-born players. The results need not imply discrimination per se but are consistent with the primacy of the college draft in player hires and, conversely, a downgrading of experience and backgrounds of foreign-born players who did not attend a US college. In addition, as Groothuis and Hill point out, the greater attractiveness of basketball leagues outside North America could represent a significant “pull” factor for foreign-born players. This merits further analysis.
Focusing on the effects of race on NFL quarterback survival rates with a variety of hazard function estimations, Volz (2017) finds that Black players have a greater probability of exit from NFL relative to Whites. Volz argues that Black quarterbacks are shown “less patience” than observationally equivalent White quarterbacks. Black players are less likely to be starters and more likely to exit the league. Moreover, there is some tentative evidence that Black quarterbacks suffer less exit discrimination in areas with a greater proportion of Black residents in the population.
Two papers offer evidence on hiring discrimination outside of North America. For Australian Rules football, Mitchell et al. (2011) find that performance evaluations of indigenous Australians are higher than for nonindigenous players. The player ratings here represent expected performance; indigenous Australians deliver performances that on average exceed expectations. For Uruguayan soccer, Gandelman (2009) models player performance with a race dummy included and finds that non-White players deliver better performances than White players. If the two groups share the same talent distribution then this would imply discriminatory treatment of non-White players in hiring. However, the crucial assumption of similar talent distributions is not tested.
Overall, the evidence of hiring and exit discrimination in various leagues looks stronger than the evidence for salary discrimination. Results vary by league and the sources of hiring and exit discrimination need further analysis. In particular, the processes of integration of particular ethnic groups need closer attention. Another important consideration worth pursuing is the impact of player survival on career earnings and whether Black (or other ethnic group) players suffer on this measure relative to White players.
Player Mobility and Player Draft
Twenty-two papers in
Sports economists have long been fascinated by the Coasian Invariance Proposition, first stated by Rottenberg (1956). Processes governing the movement of players, such as the reserve clause in North American sports leagues, should not affect the allocation of player talent across teams. In an invited contribution in the first issue of
Krautmann (2008) offers an alternative perspective on the Invariance Proposition with recognition of several obstacles to Rottenberg's assumptions. These assumptions include a lack of externalities that might affect team owners’ hiring choices. Without a reserve clause, team owners in large markets would bid for elite talent and, assuming a fixed talent supply, this puts small market teams at a competitive disadvantage. If fans respond adversely to the resulting lack of competitive balance, then league-wide revenues and profits are reduced. Supported by a reserve clause policy, team owners can discipline themselves to mitigate the external effects of their hiring choices. Other assumptions that might not hold are negligible transactions costs and players not considering nonpecuniary net benefits such as preferences for choice of location. Krautmann (2008) questions the assumptions behind the Invariance Proposition and suggests that players do not necessarily end up with teams that value their talent the most.
Depken (2002) shows that MLB free agency in 1976 had limited effects on the concentration of player talent. Using Herfindahl–Hirschman concentration indices over 1920-2000, Depken finds a reduced concentration of home runs but not strikeouts or runs scored in the period after free agency.
A further questionable assumption behind the Rottenberg Invariance Proposition is a fixed supply of talent. Using a similar data set to Depken and deploying unit root tests, Schmidt and Berri (2005) find that dispersion in player performances fell after free agency and they attribute this to an expansion of the baseball talent pool as teams widened their player search geographically. The effects of the entry of baseball players from Caribbean, Latin American, South American, and Asian countries on the player labor market have surprisingly not been considered so far in
Restrictions on player movement in soccer were fully loosened with the Bosman ruling of 1995. In line with the free movement of labor throughout the European Union, footballers could move freely within and between European soccer leagues after the expiry of their contracts, whereas previously clubs could demand a transfer fee as compensation even if a player was out of contract. After the Bosman ruling, player pay accelerated in a similar pattern to MLB free agency (Dobson & Goddard, 2011).
In soccer, player mobility increased, both between and within leagues. Two
An analysis of assortative matching that conforms to standard labor market applications, such as Abowd et al. (1999), is offered by Drut and Duhautois (2017) for Italy Serie A. From player wage equations with panel data over 2009-2014, the authors extract player and team fixed effects. The significant positive correlation between the two sets of fixed effects indicates positive assortative matching. Moreover, player fixed effects show a greater correlation with log wage than team fixed effects. This indicates the presence of superstar effects in Italian football. Outside of soccer, Peeters et al. (2020) find evidence of assortative matching in the market for field managers and general managers in MLB.
The standard theory of labor migration proposes that net of monetary and psychic costs, workers move between locations dependent on wage differentials between host and sending regions or countries (Borjas, 2020, ch. 8). Within North America, States and Provinces have different average and marginal rates of income tax. This variation is exploited in two papers in
Lack of mobility for drafted players and relatively small sizes of major leagues in North America jointly result in monopsony exploitation of young players with pay below marginal revenue product. Following Scully (1974), the standard approach to the estimation of marginal rates of exploitation entails first, regressing team wins on player performance inputs to determine marginal productivity and second, regressing team revenues on team wins to convert marginal physical product into marginal revenue product.
In a rare analysis of a female sports league in a
In a refinement of the Scully model, Fort et al. (2019) estimate marginal rates of exploitation in MLB through the team revenue distribution using quantile regression. Applications of the Scully model to team monopsony power typically take total revenues as determined by team wins at the revenue means, using OLS. Quantile regression estimates show lower marginal revenue product and marginal rates of exploitation for smaller revenue teams. Conversely, marginal rates of exploitation are higher for larger revenue teams. At median revenues, pitcher and hitter marginal rates of exploitation are estimated at 0.78 and 0.83, respectively, in line with earlier estimates, but there is considerable variation in numbers both between teams and through the revenue distribution.
Several papers in
The college sports system provides future professional players with both a human capital element via college experience and a signal of future potential, based on the sports program reputation of the college. For NBA draftees, Groothuis et al. (2007) find some support for both human capital and signaling components. In their wage equation for NBA rookies for 1997 and 2002, college experience variables are significant predictors of rookie salary. By drafting players early in college, teams can lengthen rookie contracts to help them pay for general human capital. If a team captures a star player early, it can exploit economic rent for more years if the player is a college junior. However, identifying a future star player is of course very difficult.
Especially in MLB and NBA, players can choose whether to enter after high school or during college. This raises the question of whether expected career earnings in the chosen sport exceed opportunity costs for the draftee. Pifer et al. (2020) use a novel machine learning method to evaluate the expected career earnings of MLB draftees. Their procedure follows three steps. First, the software delivers probabilities of a player appearing in seven different classifications over his early career, ranging from MLB to permanently out of professional baseball. Next, financial data and predicted probabilities are used to estimate the expected salary over a player's first six seasons. Finally, the player's expected income is compared to those initial players who did not sign professional contracts. On this basis, Pifer et al. compute the threshold draft pick number at which a player is indifferent between signing a professional contract and staying out of the sport. Earnings outside of baseball are total six-year incomes for 18- to 24-year-olds according to educational attainment.
For picks below the threshold, a signing bonus or high expected performance is needed to offset the opportunity costs of playing baseball. For example, the threshold for pitchers with some college experience is pick number 171. For college graduates, the threshold rises to 32. Pifer et al. (2020) suggest that young baseball players may be unrealistically optimistic about their chances of success. The prospects look especially gloomy for players who are stuck in Minor Leagues as pay there is very low, and players are exploited even more than in MLB. This raises a concern for MLB. The draft selection process leads to the development of general human capital in Minor League teams supported by monopsony exploitation of rookies (Krautmann et al., 2000). However, pay at Minor League teams may not cover a player's reservation wage especially if the player is a college graduate. Moreover, star players are often multitalented and have choices over which sport to enter. Then, the relative severity of rookie employment contracts in different sports may play a role in player choices. This point has not been explored in research so far.
Concluding Remarks: What Next?
Papers on sports labor markets published in
It is clear that player pay responds to lagged player performance in most leagues studied in
An important line of inquiry to follow here is the connection between broadcast rights deals for sports leagues and their impacts on player pay and contracts. In soccer and NBA especially, overseas sales of broadcast rights have grown in value over time, partly driven by the appeal of particular star players. If superstars capture much of the rents from overseas broadcast rights, how does this affect other players? Do they respond positively with the expectation that high-earning teammates will help them achieve team performance objectives such as playoff appearances and Champions’ League success? Alternatively, do envy and lack of team cohesiveness appears with damage to team morale and team performances? In soccer leagues, it is often alleged that “arms races” develop where teams overbid for player talent in an unconstrained quest for team success. Can this be ascertained at the player, rather than the team, level?
The emergence of documented high-frequency play-by-play data should facilitate the study of productivity spillovers between teammates. The finding of Arcidiacono et al. (2017) that productivity spillovers affect team output but not individual pay is specific to NBA. Does this result generalize to other leagues where player roles are more specialized, such as NFL or MLB?
Research in
Research in
It is difficult to apply difference-in-difference analysis to sports labor markets. This is because changes in rules and regulations in sports labor markets typically affect all teams at the same time. A future study on player movement in European soccer leagues could draw upon the recent exit of Britain from the European Union and associated variations in work permit rules for players across Europe. Although free movement of players within the European Union, minus Britain, remains a core principle there are various work permit restrictions applied to immigration of players from outside the European Union.
Papers in Machine learning methods such as Lasso and Random Forest to identify relevant player productivity effects from multiple measures; Searches for instrumental variables in pay–performance and pay–performance–contract length relationships; Propensity score matching methods to identify effects of ownership and head coach changes and other endogenous impacts on player careers; Application of player fixed effects in pay–performance models; Estimation of unconditional as well as conditional quantile regression models of player pay (Carrieri et al., 2018); Estimation of staggered difference-in-difference models of player pay and performance where events such as Covid-19 infections occur at different times; Competing risk models of player career duration.
Armed with these contemporary techniques, the future for scholars working on professional sports labor markets looks very bright.
Footnotes
Acknowledgments
The author thanks Bernd Frick and Brian Mills for helpful comments on an earlier draft.
Declaration of Conflicting Interests
The author declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Funding
The author received no financial support for the research, authorship and/or publication of this article.
