In sport, the roster is the pool of players available, and the squad it the selection of who who might be used in a game, tournament, etc, including the reserves who may or may not play.
Speaking about American football, you have a 53-man roster. These are the players who are suited up and available to play in a game.
"Squad" could refer to the entire team and thus be synonymous. Or it could refer to a subset, like the offense or the defense. There's even a "practice squad," a set of player who are not on the roster, but practice with the team and are available to join the roster in cases of serious injury.