Aggression from Cockerels is perfectly normal and natural behaviour, if a little 'inconvenient'. The Tamer the bird, the more aggressive he is likely to be. Birds with a healthy respect/natural fear of their owner are not likely to become ' Man-fighters'. the whole framework of Chicken society is based on aggressive behaviours. They fight from chickhood, heirarchies are decided by aggression, access to the choicest morsels and best roosts are all decided by varying degrees of aggression, from a fixed 'stares', body posturing, Fanned or raised plumage, vocalisations, Feinted Strikes, to out and out Beak claws and spurs combat!! When a formerly tame male turns Man-fighter, don't take it personally, it's quite a complement in a way?! He regards you as part of his Social group, and so he will attempt to assert his dominance over you. Like-wise if you tamper with his females or offspring, he will do what comes naturally and attempt to drive you away. Never respond with aggression! this will only serve to escalate his anger and entrench the behaviour further. Catching and holding can work in some instances, as can squirting with a water Pistol, both are 'shock' tactics that are not part of a bird's set of natural responses, and it may knock their confidence sufficiently for them to regard you with more respect. Penning a Male in new and strange surroundings away from his females can also snap him out of his aggression. Allowing strangers to feed, water and move amongst the flock can also heip. Familiarity breeds contempt in Cockerels, and most are suspicious of strangers, and will keep a respectful distance. So a new face in the routine may take the edge of his over-confidence. Unfortunately, some birds will never calm down, and where Children ,Elderly people or pets are at risk from larger, stronger males, the offender needs to be permanently confined or culled.