I found out the hard way (sorry, RIP Doody) that males are territorial and when they fight they go for the testicles. I thought my two male rabbits were getting along great in their cage until one day I saw Doody had been castrated the hard way! SIGH We took him to vet, but he didn’t make it through the night because of shock.
I had actually considered frostbite, because we had an extremely cold winter. But the two winters before this have not been so cold and one time, in the summer, the bunny had freshly bloody ears, so that would not be frostbite. I have been watching these chopped up ears for several years. We do have feral cats around here, and coyotes. A coyote would take the entire bunny, but I could see a full grown rabbit putting up a big fight with a cat.