when they show who is playing where, why do some players have a number beside them?

Answer 1

Don't know exactly what you are asking but they will sometimes highlight a player, or two, and give their batting average or highlight what that player has done against the pitcher this year, or lifetime. It's just statistical information to help you enjoy the game with a little insight of interest.

Answer 2

Each position in the field has a number - pitcher is 1, catcher is 2, etc.