Did you ever see a student been physically restrained by recess supervision in order to break up a fight? Was it helpful to deescalate?

Yes, I have seen physical restraint of one student in a fight. It stopped the immediate altercation, but it certainly didn't help to de-escalate the bad feelings. It just frustrated the aggressor and made him feel he had been treated unjustly. Sometimes restraint can work if the students are really out of control and both of them have been restrained [requires more personnel], which gives them more of a feeling of equality against a common foe. But in general it's better to solve it through verbal separation and cool-down, followed by skilled counseling by someone other than the recess supervisor. Someone who knows how to listen and interpret.

The first responsibility of the supervisor is to prevent any child from being injured. If that requires restraining another student, that's the first thing to do. Then the supervisor can attempt to deescalate the situation.