That's.. Nothing unusual for rodents. When my female mice have spats they end up making each other bloody. I have one mouse with only two usable legs and most of his tail gone from when a mouse gnawed on him as a baby. Mom wanted to keep him as a pet and call him "stumpy" x.X Hamsters are worse than mice. They're very "I like my personal space 'rawr!'". Especially the females. Unfortunately for pet stores, you can't have a hamster per tank simply because you'd spend more money on bedding and more time feeding/cleaning/watering. Plus it'd take up more room.