How to control my frustration at my softball game?

I get frustrated really easily at my softball game. I'm the pitcher and whenever the opposing team gets a hit, sometimes the defense is really good and sometimes they give up on me and field and throw the ball very sloppily. It gets me really fustrated and it affects my pitching. The team we play tonight is the game that will determine who makes it to the play-offs. So I'm taking this game very seriously. How can I control my frustration?