Can I call faults on my opponents?

Only two kinds: non-volley zone (kitchen) faults and service foot faults (Rule 9.B.3).

• Call them as soon as you see them, and before the next serve.
• If the two teams disagree about the fault, the rally is replayed.
• If partners disagree, the call goes in favor of the opponents.

For any other fault you think an opponent committed (for example, the ball touching their shirt), you can mention it after the rally, but you can't enforce it. The final decision belongs to the player who allegedly committed it (Rule 9.B.4).

Players are expected to call faults on themselves and their partner as soon as they know about them (Rule 9.B.2).