A baseball game will feature nine (or ten, if you have a DH) players on a team, but let’s look at how a typical roster is constructed.
In Major League Baseball each team is allowed to bring 25 players to a game, all of whom are eligible to play. It’s super rare that all of them will, however. There are no stipulations for minimum or maximum players in any given position, but teams will generally look something like this:
Nine position players – These are the guys in the starting lineup who will play most days. One or two may swap out consistently with a backup or bench player depending on how well they hit left- or right-handed pitching. A “position player” is a non-pitcher.
Five bench position players – These are backups who might come into the game at some point. Some will only play one position, while others called a “utility man” may be proficient in multiple spots.
The starting rotation – Almost always will consist of five pitchers. These are the guys who will start every game, meaning they will only play once every five games, and try to pitch as long as they can. The best pitchers, or at least the ones with the most stamina, are usually starters.
The bullpen – The balance of the team will be relief pitchers. These guys will enter the game after the starter is pulled and will often have loosely defined roles like long reliever (who will throw more innings if a starter gets knocked around early), closer (who will typically be the best pitcher in the bullpen and pitch the ninth inning), or the setup man (who will come in right before the closer). The “bullpen” is the name of the physical place where the relievers warm up before they come into the game, but it’s also sometimes used in reference of the relief pitchers themselves.