What smashes into Piggy and kills him?

Piggy is crushed by a boulder shoved by Roger down the mountainside. Ralph manages to dodge the massive rock, but Piggy is not as lucky. The rock crushes Piggy and throws him off the mountainside. He lands on the rocky surface below and dies.
Ralph, Piggy, Sam, and Eric go to Jack’s camp to recover Piggy’s glasses that had been taken by Jack’s group. When they arrive, they meet guards at the camp. Shortly after, Jack and the hunters show up with a dead pig. A confrontation ensues between Ralph and Jack. Ralph tries to reason with Jack to give them back the glasses so that they could reinstate the signal fire. However, Jack calls for the capture of Sam and Eric. A fight ensues between Ralph and Jack. Piggy tries to speak, but Roger shoves the boulder, which kills him.