 When each major league baseball game starts there will be nine or ten players in each team starting lineup nine in the National League Where the pitcher hits for himself and ten in the American League or a player called the designated hitter hits for the pitcher It's very rare. However, that all of those players will play the entire game So let's look at how rosters work and which players are eligible to play in any given game Let's say it's a National League team So we have a nine man starting lineup these nine players are chosen from a 26 man act of roster So each of these 26 players are with the team and are eligible to play on that day Typically a major league roster is comprised of something like 13 or 14 pitchers Which in turn are made up of five pitchers who are called the starting rotation These pitchers will be the ones who pitch first for their team in a game and usually try to pitch for as long as they Can there will also probably be a closer who will pitch at the end of a close game a Setup man who will pitch right before the closer and the rest of the pitchers are just relief pitchers a Typical game might look something like a starting pitcher pitching the first five innings a middle reliever pitching the six and the seventh a Setup man throwing in the eighth and a closer pitching the ninth other than pitchers We have position players which will probably include something like two catchers five or six infielders and four or five outfielders These are not official designations from a rules perspective all we care about is having 26 players So a player who is typically an infielder is allowed to play any position But this will hopefully give you a general idea of the makeup of most teams When it comes to a major league franchise Each one will not only control their MLB team But also has contracts with a number of minor league teams where that franchises younger Potential future players will play we won't get into how the minor leagues work much But it's important to know that they are there as a player progresses his way up through the lower leagues The franchise may place him on what is called the 40 man roster So while the 26 man active roster is comprised of the players who are allowed to play in that major league game on any given Night the same 26 players probably will not make it through the entire season If a player has a minor injury, he'll probably just not play for a few games But he's still considered to be on the 26 man roster meaning he's taking up a spot and he can't play Which isn't good for a few days. This probably isn't that big of a deal But keep in mind that major league teams play a game almost every single day So for something longer term, obviously it can become an issue That's why there's something called the injured list or the IL a Position player who is hurt can be placed on the IL But then he cannot play for at least 10 days and a pitcher cannot play for at least 15 There's also a 60-day IL for longer term injuries being moved to the IL keeps a player on the 40 man roster But frees up a spot on the active roster that can be filled by another player on the 40 man roster Most likely one who was in the minor leagues a player on the IL can do his injury rehab with the team He can travel to all the games and even sit in the dugout each night if he wants to he just can't play This is how things work for most of the season with most players staying on the active roster Unless they go in the IL and then there's also a special seven-day concussion lists That only applies to concussions and there are also shorter paternity and bereavement lists That also will free up an active roster spot for a few days If a player has a family member either entering or exiting conscious existence Late in the season on September 1st Rosters expand so the teams can have an extra two players on their active roster so 28 rather than 26 These few weeks are referred to as September call-ups and until a few years ago Teams would be allowed to add their entire 40 man roster to the active roster This achieved its intent of allowing younger players to get some playing time in the major leagues But it often created this weird scenario where some teams would have 10 more players than the other team Not to take it all play, but it just became too big of a difference. So now it's 28 no more no less After the regular season when things move on to the postseason Teams are limited again to a 26 man active roster that is chosen at the beginning of each playoff series In baseball the playoffs consist mostly of best of five or seven game series Although they can be replaced for the remainder of a series by another player on the 40 man roster if one of them were to get hurt So that pretty much sums up MLB rosters teams have a 26 man active roster To choose their nine or ten man starting lineup in their subs on any given day from if one of those players is injured They can move to the IL for at least 10 or 15 days depending on their position At which point they can be replaced by another player on the 40 man roster Who will most likely be called up from the minor leagues rosters expand to 28 players in September? But then decrease back down to 26 for the playoffs