How old is he? Is he an immature cockerel or a mature rooster? There can be a huge difference in their behaviors and the hens' reactions. You don't get guarantees with living animals because they all have their own unique personalities so anything can happen. Usually introducing a mature rooster to a flock of mature hens is about as easy as integration gets. Usually. Typically he swaggers in, impressing them with his magnificence and self-confidence, mates with one or two, and it is his flock. It's possible the dominant hen doesn't want to give up her position as flock master so she puts up a fight (mostly more running away than actual fighting) but it can get violent. If he is weak and doesn't have that swagger the hens are much more likely to resist him. You always need a plan B in case it doesn't go well, but usually it is pretty easy.
If he is still an immature cockerel he is a lot less likely to impress them with his magnificence and self-confidence. The older hens, especially the dominant hen, may beat him up pretty badly and make his life miserable, possibly endangering him. He may try to force them which can lead to violence or it may be more chasing and running away. If you have a lot of room it can work out, but with an immature cockerel there is often a level of violence that is hard to watch. Sometimes, even in tight quarters, it isn't that bad. It's just that way with living animals, but always have a plan B in case. The personalities of the hens has a lot to do with it too, not just the male.
I don't believe in magic numbers when it comes to male/female ratios. My main breeding/laying flock is typically one rooster with 6 to 8 hens. I generally don't have those issues. The rooster is generally mature. I've had more problems with higher numbers of hens but I have a unique way of dealing with it when it does show up. I eat the hen. That gets her genetics out of the gene pool. I very seldom have these problems with the pullets I hatch. If I reduce that hen/rooster ratio (which some people think would make it worse) and the problem goes away I don't blame the rooster.
