Innings pitched


In baseball, innings pitched are the number of innings a pitcher has completed, measured by the number of batters and baserunners that are 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 counts as two-thirds of an inning. Sometimes, the statistic is written 34.1, 72.2, or 91.0, for example, to represent innings, 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'll throw one pitch which will result in a triple play, and for that one pitch he'll be credited with a full inning pitched.

Decline

The only active players in the top 100 all-time at the end of the season were Tom Glavine, Randy Johnson, Jamie Moyer and John Smoltz. By the end of the season, only two active players were in the top 100 all-time: CC Sabathia, and Bartolo Colón. This is because over time, innings pitched has declined. Several factors are responsible for this decline:

All-time leaders

Single season leaders

Per Baseball Reference:
RankPlayerYearTeamInnings pitched
1Ed Walsh1908Chicago White Sox464
2Jack Chesbro1904New York Highlanders
3Joe McGinnity1903New York Giants434
4Ed Walsh1907Chicago White Sox
5Vic Willis1902Boston Beaneaters410
6Joe McGinnity1904New York Giants408
7Ed Walsh1912Chicago White Sox393
8Dave Davenport1915St. Louis Terriers
9Christy Mathewson1908New York Giants
10Jack Powell1904New York Highlanders