I have had cows and bulls that were over protective. More cows than bulls. If a cow started pawing and swinging her head, I would get a big limb and start walking towards her very fast then send what ever I had in my hand at her and that always has made them run other way. Then the next time I went in the pasture, I would find the same cow and walk to her briskly and throw something at her again. If I had to do it a few times, I had to show her who was the lead in the pasture and it was me. When you hunt her down first, then she wants nothing to do with you.
If she is a really good cow, then it is worth it. But if she is narrow and a hard keeper, low to middle calves, she is gone as well.
I think when you are the aggressor, and head towards them before they come to you, they leave.
Bulls that have been slightly showing aggression, it worked as well. But if I had one that was more protective, I would ride my 4 wheeler to him and waving and yelling at him. Get off the 4 wheeler but stay close and keep waving a stick that is taller than him. If you are above his head with a pole, I think the height thing works. Get a shovel handle and hurl it at him and make him keep moving.
If it takes a few times, it works, as they are not sure who is lead in the field. It is nature. If you don't establish who is boss, then they can hurt you when you really have to work with them. I know people get killed by cattle. But they will try you if they are protective which is actually a good thing for the herd if you are in an area of predators. His brain tells him to protect the herd. I had one bull that would run across the pasture if the neighbor dogs came in. Then some of the cows follow and the calves too. They all learn how to protect the herd from the strong minded ones. That is just how I see it. I like it when my cattle are protective.
If this is a really good bull, he gets to stay, but if he is a crap bull, I would send him to the sale barn.
Yeah, I am nuts. But this has always worked for me.