Introduction
Baseball is a popular sport worldwide. In the USA only, 15.64 million individuals participated in baseball in 2017.1 Strength and power are most certainly crucial physical qualities that characterise every elite baseball player and are considered central to the development of successful young baseball players.2 Three key basic skills need to be mastered for players to play at an elite level: running, batting and pitching. For the latter skill, ball velocity is considered an important performance parameter sought after by recruiters and coaches.3 The throwing motion, however, is a complex motor skill, which can be divided into six distinct phases: windup, early cocking phase, late cocking phase, acceleration, deceleration and follow through.4 To achieve high ball velocity, it is believed that the global throwing motion needs to be properly, if not perfectly, executed.5 Typical baseball throwing motion phases are presented in figure 1.
Most published scientific studies have focused on ball velocity, because it is easier to assess than other pitching parameters. Ball accuracy, however, also seems to be an important factor when assessing pitching performances. According to Kawamura et al,6 a player showing high ball velocity but poor throwing accuracy will not have better outcomes than other pitchers. Kawamura et al used three different methods to assess pitching accuracy: pitch location accuracy, pitch location trajectory, and finally, the distance and the direction of the errors from the target position.6 The authors proposed that those methods are reasonable and sufficient to assess pitching accuracy.
Finally, the performance of the pitcher can also be easily evaluated using game statistics.7 For instance, Whiteside et al used the fielding independent pitching (FIP), an indicator focusing solely on the events a pitcher has the most control over,8 as an indicator of pitching performance for players from the Major League Baseball (MLB)9 and players from the National Collegiate Athletic Association.10 Specifically, they used statistics unique to pitchers: home runs (HRs) conceded, number of unintentional walks (BB), number of pitches that hit the batter (HBP), strikeouts (K) and number of innings pitched (IPs) to assess pitchers’ performances. The lower the value of the FIP, the better the pitching performance is. Alternatively, using a different approach to game statistics focusing on the number of IPs, strikeouts per inning (BBin), walks per inning, walks plus hits per inning pitched (WHIP) and batting average against (BAA), Chaudhari et al investigated the correlation between lumbopelvic control and individuals’ pitching statistics.11
Ball velocity, accuracy and game statistics represent three methods used in combination or separately to objectively measure pitching performance. To the best of our knowledge, no study has summarised nor systematically assessed the scientific evidence regarding factors associated with pitching performance. Given the various methodological approaches identified to assess pitching performances and the wide range of potential individual and technical indicators of pitching performance, it is believed that a better understanding of individual determinants of a pitcher’s performance could help coaches focus on specific aspects of training and improve athletes’ performances. Therefore, the aim of this study was to list and classify performance factors associated with baseball pitchers’ performance, to describe the methods used to assess pitching performance through all features of the game, and most importantly, identify individual factors associated with baseball pitching performance through a scoping review.