They all seem wild and crazy first, but it is all part of what they are meant to do, and the hens are not innocent bystanders. The behavior of 'rooster chasing hen all around the yard' has purpose. At first you'd be forgiven for thinking that the hen has no interest in mating but that is not so. She does, and if you watch carefully, you'll see that she is making sure that the rooster is up to the job of being number one, or at least incredibly brave. A lot of the time, when other roosters or predators like dogs or people are around, the hen will run past each and every one of them first to test the mettle of the prospective rooster. If he chickens out when she runs past another Rooster, he was scared of that rooster, or dog, or whatever. If he succeeds in his chase, well, she knows what she knows and knows he's the best, or good enough till the best arrives. This is only one of many mating rituals though, and some are not nice.
A torn up back means a hen can look forward to huge, strong chicks and isn't that worth it ? she thinks so.