I’m not keen on having players stop play to call faults like this. They don’t do it in rec play and most likely won’t do it with a referee. Allowing fault calls on the opponents will open the door to players calling foot faults (i.e. push offs, ernes) on their opponents. Players may agree that calling faults on the opponents takes away from the concentration on the rally. Furthermore, you are allowing the players to make calls that could be considered judgmental. This has the potential to lead to additional conflicts amongst the players that the sport does not need. Let the players play and the officials officiate.