Runner on third. after the pitcher begins his windup or motion to the plate, the batter jumps out of the box and yells time. If there's a good ump, he will not award the batter time because the pitcher is already in his wind up. The pitcher will be startled and not pitch the ball, which is a balk, and the runner scored. A team did this to us many years ago and I was not very happy. Bush league, but a trick play nonetheless.
Another is when there are only two umpires, one behind the plate and one in the field, runners on second and third the hitter puts down a bunt. The home plate ump should be watching the runner cross the plate and the field ump should be watching the play at first so the runner on second and cut third WAY short through the grass and there, you have two runs on a bunt. Once again, someone has done it to a team i've coached and I was not very happy...BUSH