Give them a plan verbally when they have two strikes, one that replaces the negative and timid thoughts in their heads.
Could be as simple as saying "make contact."
Many of the things we say create negative thoughts, such as when a batter has two strikes or a pitcher has 3 balls.
Boy this could be its own thread. Things not to say for successful players. My 2 least favorites are with a runner on 3rd
Coach to pitcher: Make sure you cover on a wild pitch or passed ball.
Coach to catcher: You better block the pitch in the dirt