What is the minimum temperature that baseball can be played at?

Answer 1

There is no absolute limit. The head umpire (or, if a World Series Game, the Baseball Commisioner) can call a game if weather makes the field "unplayable."

Note that it's the field, not the players, that are important. Player discomfort is a case of "too bad;" a field that is rock solid due to frozen dirt would probably be called.