How do the boys react to piggy? What "role" does he play?

Unfortunately Piggy is the only person who unites the boys. He is the focal point of derision. Except for Simon and perhaps Ralph (later on) the boys can all come together to humiliate Piggy. Although Piggy is the smartest boy on the island, he is fat and has asthma. He serves as the bully victim. Ironically if they had given Piggy more respect, they might have done much better.