Dean said 'Coop, this here umpire is a rookie and he's calling his first big league game so I want to have some fun with him. Put this baseball in your glove when you leave here and I'm gonna wind up and pretend to throw my fastball but I ain't gonna have no ball in my hand and I want you to pop your mitt with the ball like you just caught it.'
So Cooper grinned and said ' o.k. Diz'.
Diz stared in at the catcher as the batter got ready and then he went into that very-animated windup which he was famous for and went through the motion of firing that fastball of his and Cooper slammed the ball into his mitt with a loud pop.
The rookie umpire not wanting to admit that he never saw it yelled 'STRIKE ONE'. The batter, who also was embarrassed that he had not seen the ball replied 'Strike?, that damn thing was a foot outside'.
Ole Diz just stood on the mound with that big ole possum grin on his face and watched as the batter and umpire went nose to nose with their argument.
This story was told by Diz to some friends years after he had retired and he told it as the truth but now that Cooper and Diz are both gone their secret is safe forever.