<P> After August 31, during the regular season teams may call up additional personnel to the active roster, up to a maximum of 40 players . This number is seldom actually approached, however, with most teams' September rosters peaking at around 30 players . </P> <P> In the postseason, rosters are fixed at 25 men . Until 2007, teams could not replace players on their playoff rosters in the event of an injury and had to play out the series shorthanded . Starting in 2007, an injured player could be placed on the disabled list and replaced by another player who was not included on the initial 25 - man roster, but the injured player becomes available for the next round of the playoffs should his team advance . </P> <P> Rule changes have been implemented at different levels of baseball to quicken the pace of the game . In college baseball, the Southeastern Conference experimented with a 20 - second pitch clock during the 2010 season, and the NCAA instituted the pitch clock before the 2011 season for when no runners are on base . The pitch clock began to be used in professional baseball as well, first in the Arizona Fall League in 2014 and in the Double - A and Triple - A levels of Minor League baseball in 2015 . </P> <P> Rob Manfred, the Commissioner of Baseball, instituted rule changes to MLB before the start of the 2015 MLB season to address the pace of the game, including having batters remain in the batters box and the installation of time clocks to limit the time spent around commercial breaks . </P>

What determine the winner of a baseball game before 1857