Cats can make lots of noise, pull each other's hair, and roll around quite dramatically without either cat being injured. If small spats do occur between the cats, you should not attempt to intervene directly to separate the cats. Instead, make a very loud noise, or throw a pillow at or a glass of water on the cats in order to separate them. Give them both a chance to calm down before re-introducing them to each other. Be sure each cat has a safe hiding place.
Successful introductions require time and patience.