The numbers three and four appear prominently in the game of baseball. There are three strikes for an out, three outs per half-inning (i.e., teams switch after three
outs, where each first half-inning is called the "top" and the second the
"bottom"), 
innings in a game, giving 
outs per game (assuming no extra innings). In addition, there are 
players per team. Four balls are needed for a walk.
There are 
games in the regular season, 
each for home and away games.
The number of bases can either be regarded as three (excluding home plate) or four (including it).
