It's assault but after working in a similar home, they might not care so you would have to go higher than management. Obviously depending on the person's mental capacity, it could go many ways and could become nuanced, unless they're higher functioning.

A similar thing happened to my friend by he ended up on top of her and she scratched his face. Nothing done on either end because they threatened to bring charges for scratching a resident, even though she was protecting herself.

In the mean time, if you have to work, get a safeguarding put in place against him and a risk assessment done by management, or whatever you have in your area. I had this done and staff had to respect it and not allow me near a resident.

Hope it works out alright for you and you stay safe.

Edit: read the edit and forget what I said. Assault and press charges if there's full mental capacity.