"The phrase 'off with the crack of the bat', while romantic, is really meaningless, since the outfielder should be in motion long before he hears the sound of the ball meeting the bat"

This quote by Joe DiMaggio is referring to the phrase "off with the crack of the bat", which is frequently used to describe an outfielder's quick response to a batted ball. While this expression is frequently used to explain a great play, DiMaggio is mentioning that it is in fact worthless, given that the outfielder needs to already be in motion before they hear the noise of the ball meeting the bat. This is due to the fact that the outfielder needs to expect the ball's trajectory and remain in the ideal position to make the catch. Therefore, the expression is more of a glamorized description of an excellent play, instead of an accurate description of the outfielder's ability. DiMaggio's quote is a tip that the outfielder's skill remains in their anticipation and fast response, not in the sound of the bat.