What's the best way to stop a baby who breastfeeds from bitting/playing with the nipple?

Firstly I've learnt that reacting in a very big way by saying ouch only makes her bite harder because she thought I was playing with her! You should unlatch immediately when he bites and tell him firmly that if he bites he will not have any milk to drink. Another way is to maintain eye contact or play finger games with him while nursing. Singing a song may also work.