When pitching you are normally only able to choose from a "fastball" and a "split". Hold Left, then rotate the D-pad clockwise and press B to unlock the rest of the pitches.
Choose your hit
When batting, there are five ways to hit the baseball.
Grounder: Press Down + B.
Homerun (sometimes): Press Up + B.
Left Field: Press Left + B.
Right Field: Press Right + B.
Random Hit: Press B.
Double play after a walk
Sometimes when a batter walks, he will stay at home plate and not go to first base. You (or the CPU) can make a double play if the next batter pops out.