I have lots of rabbits, I have never had one attack my chickens but they were extremely aggressive towards each other sometimes. I had a small buck who killed multiple other larger and stronger bucks, he would rip into their chests and attack their faces and would hunt them down if I did not split them up well enough. I have had a few of these bucks in the past, the most horrible one broke into my breeding pen and killed the alpha buck and young bucks and even a few babies. The females can be pretty aggressive too but I have never had one that killed other rabbits. I have had a female who would attack me if I got near her babies, she could put a pretty big gash in my hand if she got lucky.