OK, then define necessary precautions. Would any crowd watching fall under the officer’s purview of being able to take necessary precautions?
In my opinion, watch but not interfere.
A cop has to make split-second decisions as to what to do in any situation and he’s not always going to make the right ones. But it’s best if the cop has determined an arrest is necessary to let it happen peacefully.
You can always address any inadequacies in lawful ways.