After you hit a base hit, wait until the fielder throws the ball over to second base, then press L to keep running. The second baseman should throw the ball to first base and give you the chance to steal second.
Note: This works most of the time, but only with the faster runners.
To get a mascot costume you have to beat the game in season mode without losing. You get the costume of the team you beat it with.
While you are in exhibition mode and picking a team press L + R and you should get more outfit selections.
If you bunt foul on strike three, you are called out. However, the out doesn't count toward your total---you have the same amount as you did before you bunted!