Usually when that' going on you have some environmental factor (either something they see or hear) that is causing one of the birds to be agitated then that bird riles the others.
First though check all the hens to see if any have sores on their back, heads, or feet. If they do they will become aggressive when the male tries to mount them.
Coturnix quails' minds hang by a very thin thread, and environmental factors can cause that thread to snap pretty easily. They particularly hate things like; flapping plastic sheeting or tarps, running water with no other background noise, loud exhaust on cars/trucks, wind chimes, or any of those sorts of things. They also get agitated like that when people spend too much time around the cages, if they aren't used to that.
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