In baseball, the statistic innings pitched (IP) is the number of innings a pitcher has completed, measured by the number of batters and baserunners that have been put out while the pitcher is on the pitching mound in a game. Three outs made is equal to one inning pitched. One out counts as one-third of an inning, and two outs as two-thirds of an inning. Sometimes, the statistic is written 34.1, 72.2, or 91.0, for example, to represent 34 1/3 innings, 72 2/3 innings, and 91 innings exactly, respectively. Runners left on base by a pitcher are not counted in determining innings pitched. It is possible for a pitcher to enter a game, give up several hits and possibly even several runs, and be removed before achieving any outs, thereby recording a total of zero innings pitched. Alternatively, it is possible for a pitcher to enter a situation where there are two runners on base and no outs. He could throw one pitch that results in a triple play, and for that one pitch he would be credited with a full inning pitched.

Decline

In Major League Baseball, the only active players in the top 100 all-time at the end of the 2009 season were Tom Glavine (ranked 30th with 4,413 1/3 IP), Randy Johnson (ranked 38th with 4,135 1/3), Jamie Moyer (ranked 45th with 3,908 2/3) and John Smoltz (ranked 74th with 3473). By the end of the 2018 season, only two active players were in the top 100 all-time: CC Sabathia (ranked 73rd with 3470), and Bartolo Colón (ranked 74th with 3461 2/3). This is because over time, innings pitched have declined. Several factors are responsible for this decline:

Records

All-time leaders

Single-season leaders

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