He protects the conch.
Jack took Piggy's glasses.
Jack and his followers steal piggy's glasses.
Roger and Maurice are the ones that attack Jack and Piggy because Jack wants Piggy's glasses.
piggy's glasses
After Jack leaves to go to Castle Rock, Piggy becomes more confident with himself, and starts to stand up for himself. This happens because Jack stole Piggy's glasses, and now he can no longer hide behind his disability of not being able to see.
Piggy
When Ralph first spots the conch in the lagoon Piggy tells him, "I knew a boy who had one of those, on his garden wal it was, they are ever so valuable." He later tells Ralph that the boy, "he used to blow it to make a noise," and explains to Ralph that the boy blew from his diaphragm in order to get a noise from the conch shell. So although Ralph actually finds, recovers and blows the conch. Piggy identifies it correctly and informs Ralph that it can be blown.
Jack initially dismisses Piggy and the influence he has on the group. He belittles Piggy's intelligence and continually undermines his authority in order to maintain control over the other boys on the island. Eventually, Jack's treatment of Piggy escalates into physical violence, culminating in Piggy's tragic death.
Jack orders the boys to kill Piggy and Ralf.
When Jack said he didn't hunt, Piggy mocked him by saying that Jack couldn't hunt as he was just a boss. Piggy implied that Jack was incompetent and only good at giving orders, not actually participating in the hunting.
Both Jack and Piggy, are stubborn English boys of about 12 years old and symbolically represent groups of society and parts of the human thought, but Jack and Piggy's similarities end there
Jack and his tribe.