You've been getting some pretty good answers here. I'll try to add a little.
Some roosters are good and some are not. Some hens are good and some are not. Bad is usually more noticeable in a rooster because he is so big and strong.
A rooster has two basic instincts, protect his flock and make sure all eggs are fertile. Everything else he does is related to those two instincts. A good rooster will give his life to defend his flock. The one I have right now is not real strong in that department. As soon as I can raise a suitable replacement, he will be replaced.
A lot of what a good rooster does is related to making sure the eggs are fertile, finding them treats, breaking up fights and maintaining order, helping them find a nest, and all the courtesies he does for them. The hens are more receptive to a rooster that treats them right, keeps order in his flock, has a dominant personality, and does the things a good rooster is supposed to do. Not all roosters are good in this department. Adolescents often have the hormones raging to fertilize the eggs, but they have not yet learned that it is easier if they work to earn a little cooperation. The hens don't respect him enough to squat for him, so he forces them. That is what his instincts tell him he has to do, fertilize those eggs. The problem can be worse when the hens are actually adolescents too. They may not have developed the instinct to squat for any rooster, let alone a brash upstart. A lot of times, this problem becomes a lot better with time, but sometimes it never does.
Some people do not like to see chickens mating, even when the rooster and the hen do everything they are supposed to. It looks brutal, but really is not if it goes according to script. The rooster dances and the hen squats. (She basically is lying on the ground to spread the rooster's weight so it does not hurt her. If she tries to stand during this, his weight could hurt her legs. There is still some risk with a really big rooster and a little hen, even if she squats, but not as much as it first appears. Hens have been hurt this way though. There is some risk in say a full sized rooster and a bantam hen, but many people don't have a problem even with this.) The rooster climbs on top and grabs the back of her head. This head grab is her signal to raise her tail out of the way. The rooster quickly brushes his vent against hers and hops off. The hen stands up, does the fluffy shake to get the rooster's deposit in the proper location, and they go about their business.
It does not always go this way. Even if it goes well, it is not all that unusual for a hen to lose some feathers during this. Different things enter into that, such as the difference in the weight of the hen and rooster, his technique, her technique, and how often they mate. The problem comes in when she loses enough feathers that she can become cut. The rougher the rooster or the more she resists, the more likely something bad is to happen. I think how much room the hen has to get away if she so desires enters into the equation as well.
Some things I've observed.
The rooster dances, the hen squats, and life is good.
The rooster dances, the hen runs away instead of squatting. The rooster goes about his other business.
The rooster dances, the hen runs away and the rooster gives chase. The hen immediately squats. She just wanted to know if he was serious.
The rooster dances, the hen runs away and he chases. Pretty soon he quits chasing her. She was serious after all and not just flirting.
The rooster dances, the hen runs away and he chases. Eventually he catches her and grabs hold. She then submits. This is not really violent since she does submit.
The rooster dances, the hen runs away and he chases. Eventually he catches her and grabs hold. She still does not submit but he forces her. This is definitely violent.
All these assume the rooster dances first. Some do not try dancing first. A lot of these scenarios can happen if he does not dance first, but they are often violent. Sometimes the rooster just ambushes a hen. I don't keep these around long.
A lot of times, this gets better as they mature. The rooster's hormones calm down, he improves his technique and learns to treat his ladies right, and the hens are more likely to do their part. But some roosters are just brutes and never grow out of it. They are brutes even if the hen cooperates. Sometimes this can be a hard call to make, whether they will ever grow out of it or not. I have had a 15 week old rooster that the mature hens respected so much that they willingly squatted for him. He was a nice rooster. But I have also had some that were brutes.
What you describe sounds like an adolescent rooster, but he may be just a brute. I do not know if he will ever make an acceptable flock master. I think your approach of locking him up is a good approach. I don't know if the flock will ever get to the point where he becomes acceptable to you.