It seems to break them from their trance. Tell them it's ok to make mistakes. If they aren't making mistakes they aren't learning and trying new things. Ask them if they know who Mark McGwire is. Tell them he hit 70 homeruns in a season.
Baseball is a game of mistakes.
If they make a mistake, calmly explain to them what the mistake was. If possible, re-create the situation to see if they understand your correction. If they didn't get it, calmly explain it to them again. Have them explain it back to you. Patiently try it again.