First, young birds used to test my winter pen setup are American Games. In most, but not all instances, once a brood reaches weaning age of about 5-weeks post-hatch they go through a phase where within brood fighting becomes intense an can result actual losses of young birds. Fighting most intense with males although sometimes females get into fighting as well. Hen at such times seems a bit confused and does nothing to suppress discord. When birds kept with father / harem master, the infighting is suppressed. My standard approach has been to rear young birds in intact family units, or at least with adult males scattered about (in confinement but able to interact with young) to prevent this and also keep hawks off chicks and juveniles. This behavior usually keeps me from doing a lot of brooder rearing of games because that amplifies the problem. The broods used for this were hatched much later than I typically do resulting in very vulnerable birds going through weaning and early juvenile stage when migratory raptors (Coopers Hawks) are very abundant.
When hawk problems became apparent I penned all young birds and I did not have enough / any adult males that are through molt to pen with broods. Adult males also dump feed very badly in part because they do not seem to like mix fed to chicks. I kept broods independently violating my usual approach resulting in a lot of fighting. Stopped fighting in one brood by combing it with a smaller brood with much larger males already past the battle royal phase. That was only time I could do that. A person going by the name flypen has been using stags in same manner I have used cocks / bullstags so after brief discussion I did the same. The stag (older juvenile to nearly adult) is placed in with a brood where he does what most people detest about young roosters, he picks on younger birds. When the battle royal business is going on the stag directs his attention on the combatants and he attacks them until they back down which takes little effort. When the stag has lots of targets he causes no harm. Also, a brood in battle royal mode may also behave in a manner that makes so stag does not work them over. It takes 48 to 72 hours for battle royal mode phase to subside. Then I just leave stag with brood and he suppresses fighting that sometimes comes later. Stags fed same diet as juveniles and they are not as hard on feeders.
I cannot simply place stag on top of brood with hen as hen will often kill him in short order in confines of a pen. If she does not kill him, then she will prevent him from picking on her young doing the fighting. I have only done this four times over the last month but results very consistent.