Roger and Maurice are the ones that attack Jack and Piggy because Jack wants 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
Piggy is fully aware that Ralph is the only thing that is preventing Jack from becoming chief. Piggy knows that if Jack does become chief all hope of rescue will disappear because Jack will only bother about hunting and the signal fire wil be forgotten. Piggy is also fearful for his own safety.
Well in chapter 10 Jack and his tribe of savages invade Ralph's tribe (made of up Ralph, Sam and Eric, Piggy, and one/two littluns) in order to steal Piggy's glasses, which is overall the power to start a fire on the island. Jack might have mentioned this plan in chapter 9 so I'm hoping this is the right answer to your question.
Jack took Piggy's glasses.
Jack feels that Ralph is always protecting Piggy, whom Jack sees as Ralph's weak and dependent friend. This leads to conflict between them as Jack believes that Piggy should not receive special treatment.
Jack and his followers steal piggy's glasses.
Jack slaps Piggy so hard that it breaks one of his glasses lenses. He then goes on to mock his whining voice with his own parody of it to ridicule him. Tsch Tsch Should've Read it. All the same, your welcome.
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
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.
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.
Jack orders the boys to kill Piggy and Ralf.
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