Jack and his followers steal piggy's glasses.
No, it is Roger and the hunters who steal the conch and take it to Castle Rock in William Golding's novel "Lord of the Flies." Jack and his followers are complicit in this action, as they become increasingly savage and unruly under Jack's leadership.
Piggy's glasses
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 and his hunters break in and steal piggy's glasses
There is no attack by Jack's tribe on Ralph and his followers. Jack led a night-time raiding party, comprising of himself, Roger and Maurice, to steal Piggy's glasses in chapter 10: The Shell and the Glasses.
Piggy ran away because he was scared of Jack and his hunters, who were becoming more aggressive and violent. Piggy feared for his safety, as he was aware of the escalating tensions and the potential danger posed by Jack and his group.
No, Jack along with Roger and Maurice raided the shelters at night and stole Piggy's glasses, so that they could light fires at castle rock. The conch was destroyed, and Piggy was killed, when Roger toppled a boulder from the top of castle rock, when Piggy came to demand the return of his glasses.
They were fighting with Roger, and Jack stole fire from Piggy and Ralph.
~SPOILER ALERT~ Jack doesn't do much to Piggy other than steal his glasses in order to make a flame. Early in the book, Jack hits Piggy and breaks one lens. Later on in the story, Roger, I believe his name is, kills Piggy by pushing a big rock off the cliff and it cracks Piggy's head and he drifts off to sea.
They steal a burning branch from the fire near the huts. They steal a burning branch from the fire near the huts.
Ralph and Piggy participate in Jack's rituals because they are afraid of being excluded or targeted by Jack and his followers. They also hope that by participating, they can maintain a sense of order and control in the group.
In William Golding's novel "Lord of the Flies," it is Jack's group of savages who accompany him to steal fire from Ralph's camp. They violently attack Ralph and the other boys to steal the fire and assert their control over the island.