That is not normal. I can't tell from the picture, but if you can see the intestine layer below in that skin opening, you need to get your rabbit to an emergency rabbit vet tonight. But if you can't see the intestines and that is infection and your rabbit is eating and behaving normally, you might be ok waiting until morning to phone your vet and get your bun seen by them first thing tomorrow.
If your bun is messing with or trying to chew at the wound, you'll need to find a way to prevent him doing that. A makeshift e collar or donut collar of some sort may work.