While the grounds crew is getting the field ready for the game, the players of each team arrive to their respective dugouts. In professional games, there is usually a ceremonial first pitch. The ceremonial first pitch is thrown by a guest of honor, sometimes a celebrity or the winner of a contest. They throw a pitch from the pitcher's mound to a player from the home team who acts as a catcher.
Often times, the ceremonial first pitch is thrown by presidents, celebrities, good samaritans in the community.