I have had roosters that needed a little reeducation. I had a really good flock protector that would get too big for his britches every couple months and flare his hackles at me and lunge. He was all bark and no bite, and I'd chase him down, pick him up and hold him and give him a good inspection, turning him upside down (in front of his ladies). He'd be fine for another month or two and he'd do it again. I had to get rid of him because he scared my wife and she was not assertive enough to establish her dominance over him. I thought he was a great rooster and I was really sad to see him go. On the other hand, I had another one that shanked me from behind as I was walking out of the pen. I could have kicked a 40 yard field goal with him. The SECOND time he did it, he spent his last night in the shed awaiting culinary justice. IMO, a rooster who attacks you from behind or from the side, unprovoked, is almost always lost causes. On the other hand if a rooster stands in your path and tries to block you from the hens and lunges at you, that's a rooster being a little overzealous in his roosterly duties. Some of those can be reeducated, and may not be not "bad" roosters. They're just protective. In my experience, there are also factors that can increase aggression. Is that rooster the only rooster? Having more than one rooster together with the hens puts the alpha rooster on a constant defensive to protect his hens from being mated. People might find that the same aggressive rooster is well behaved if he's operating as the only flock rooster and can let his guard down. Do you have a dog or a child that terrorizes your chickens (chases them around constantly)? That also can also get roosters riled up and put them into protection mode. I mean, a 3 year old with a big stick IS just as dangerous as a predator, and the rooster knows it. Also, is that rooster suffering from mites or an injury that might make him more cantankerous than usual?
Like a lot of people on here have said, there's no shortage of roosters. But if you have a particularly healthy specimen who does a good job of mating the hens, treats them well, and is a good flock protector, doesn't crow at night, etc it might bear looking at the environmental factors that could potentially be contributing to his aggression. Some roosters are just bad. But there are other roosters who are simply protective and the environmental conditions you have contribute to heightened levels of aggression.
