<P> Typically, in modern - day play, an active roster will consist of five starting pitchers, seven relief pitchers, two catchers, six infielders, and five outfielders . Teams can vary this somewhat according to preference and circumstance, and indeed the "typical" roster makeup has changed somewhat over the years . (Starting rotations used to consist of four pitchers, not five, well into the 1970s; third - string catchers used to be much more common; many other minor variations exist .) In the American League, a full - time designated hitter is usually classified as either an infielder or an outfielder, not a DH, because most DHs do play defensive positions from time to time . </P> <P> Since the 2012 season, teams have been allowed 26 - player active rosters for "day - night" doubleheaders--two games scheduled on the same day, but with the stadium cleared between games, and separate tickets sold for each game--as long as the doubleheaders have been scheduled with at least 48 hours notice . </P> <P> Also called the "40 - man roster", the expanded roster is composed of all the players in a Major League club's organization who are signed to a major - league contract . The 40 - man roster limit has been in effect since 1921, except for 1945 - 1946 when it was raised to 48 to accommodate veterans returning from military service in World War II, and from 1962 to 1965 when it was raised to 41 to add a reserve spot for first - year players acquired before implementation of a player draft was approved prior to the 1965 season . </P> <P> The expanded roster includes all players who are eligible for call - up to the active roster at any given time . Also on the 40 - man are any players on the 10 - day disabled list and minor league players who are signed to a major - league contract but are on an "optional assignment" to the minors . (Each player has three "option years" to be sent to the minors once on the expanded roster before they must be placed on waivers to be sent there .) Players who were on the 40 - man but are placed on the 60 - day disabled list are taken off the 40 - man until the time on the DL is over . The same applies to players who are suspended . Because players on the 60 - day DL are taken off the 40 - man with no risk of losing the player, MLB teams often transfer injured players from the 10 - day DL to the 60 - day DL so that they can add another player to the 40 - man without having to designate a player for assignment . Designating for assignment ("DFA") is the removal of a player from the expanded roster, whereby the team has 10 days to trade the player, release him, or send him to the minors . </P>

When do opening day rosters have to be set