This is when a baby refuses to breastfeed. He will fight you, arching backwards, crying. Consider ear infection if his upset appears worse on one side or the other, or is showing any other signs of ear infection. After being treated, your baby will be more comfortable and thus, more willing to nurse. Perhaps he is reacting to a stress in the home.
Some babies are extremely sensitive and learn to associate nursing with negative emotions.
Some babies have this happen, also, if you've suddenly begun using a different deoderant or perfume that bothers him or her. The breast is soft and molds easily. Crying will put more stress on the suture line than breastfeeding. Find a doctor that is flexible and open to your nursing your baby. Sometimes this is difficult.