How do you discipline a cat that has been abused without harming him/her?

Get him a scratching pole and some toys to play with. It sounds like hes not really naughty but bored and needs something to do, or interact with. Do you play with him? Cats are very social creatures and love to play and interact with people or things. I play with mine. She chases anything that I trail along, a piece of string, a ball of wool, anything that wont hurt the cat. Ask the RSPCA or your vet what they advise.