just normal mating behaviour. Most likely he isn’t hurting them. Did you just get these chickens or have you had them all for the year? Or is this a new rooster? If it’s a young boy he may just be new to the mating and will get better with practice. If there’s no blood he really isn’t harming them. Like what the others say if you are not liking this behaviour you may want to rehire him. This sadly is what roosters do. If the girls are reluctant he will grab them. Even chase them. i can also add the more hens you have per rooster the ”easier” it is on the girls as he has more to choose from.