I have have been rearing four broods in rapid succession using pens that are up and off the ground. Not my usual approach for games, especially when under hen. Three of those broods have now gone through that fighting phase that often occurs around 4 weeks post-hatch. It is easy to parse out the voice change in chicks before battle royal commences. Now I am pretty sure some changes in the hen's voice at the same time. Her clucking less robust, almost muffled. To stop the whole mess all you got to do is put a cock nearby.
This crap can happen whether hen present or not. Same hen can have one brood that is good then another that gives me trouble. What is causing the variation? I control from genetics on dam and sire side.