A chop is a stroke that produces underspin on the ball. When the ball is short and you chop it from close range (over the table), it is called a push, not a chop. When you stand back from the table and chop, that is the typical definition of a chop.

One playing style is the defensive chopper, where the player continually chops with very heavy underspin, and the opponent will often loop, but the loops are less dangerous as it's difficult to aggressively loop against heavy underspin. It is often a test of consistency to see whether the attacker's offense is better than the defender's defense.

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