title: Changes in a Starting Pitcher's Performance Characteristics Across the Duration of a Major League Baseball Game.
abstract: OBJECTIVE
  With a view to informing in-game decision making as it relates to strategy and pitcher health, this study examined changes in pitching-performance characteristics across 9 innings of Major League Baseball (MLB) games.
  
  
  METHODS
  129 starting MLB pitchers met the inclusion criteria for this study. Pitch type, speed, ball movement, release location, and strike-zone data-collected using the MLB's ball-tracking system, PITCHf/x-were obtained for 1,514,304 pitches thrown from 2008 to 2014.
  
  
  RESULTS
  Compared with the 1st inning, the proportion of hard pitches thrown decreased significantly until the 7th inning, while the proportions of breaking and off-speed pitches increased. Significant decreases in pitch speed, increases in vertical movement, and decreases in release height emerged no later than the 5th inning, and the largest differences in all variables were generally recorded between the 1st inning and the late innings (7-9). Pitchers were most effective during the 2nd inning and significantly worse in innings 4 and 6.
  
  
  CONCLUSIONS
  These data revealed that several aspects of a starting pitcher's pitching characteristics exhibited changes from baseline as early as the 2nd or 3rd inning of an MLB game, but this pattern did not reflect the changes in his effectiveness. Therefore, these alterations do not appear to provide reasonable justification for relieving a starting pitcher, although future work must address their relevance to injury. From an offensive standpoint, batters in the MLB should anticipate significantly more hard pitches during the early innings but more breaking and off-speed pitches, with decreasing speed, as the game progresses.
authors.affiliation: School of Kinesiology, University of Michigan, Ann Arbor, MI; Institute of Sport Exercise and Active Living, Victoria University, Australia; and the Game Insight Group, Tennis Australia.
authors.forename: David
authors.initials: D
authors.lastname: Whiteside
authors.forename: Douglas N
authors.initials: DN
authors.lastname: Martini
authors.forename: Ronald F
authors.initials: RF
authors.lastname: Zernicke
authors.forename: Grant C
authors.initials: GC
authors.lastname: Goulet
mesh_terms: D000328:Adult; D056352:Athletes; D054874:Athletic Performance / Q000502:physiology*; D001484:Baseball / Q000502:physiology*; D001696:Biomechanical Phenomena; D006801:Humans; D008297:Male; D010807:Physical Endurance / Q000502:physiology*; D013997:Time Factors; D055815:Young Adult