What was the incident with the boar in Lord of the Flies?

As the boys were making their way from castle rock towards the mountain, during their search for the beast, they followed a pig run. Suddenly a boar appeared and charged them. Boys leapt aside but Ralph stood his ground and threw his spear. He hit the boar in the snout and it swerves aside, crashed through the undergrowth and escaped. Ralph was elated and related to the other boys how he had hit the boar with his spear. Typically Jack had to 'top' Ralph by showing the boys a shallow but bloody rip on his arm caused by the tusks of the boar. Jack told them he had tried to stab the boar with his spear. The boys were excited by the whole incident and spontaneously began a reenactment game. Robert acted the part of the boar and Jack shouted to his hunters, "Make a ring!" The boys began to hit Robert with the butts of their spears and then they got hold of his arms and legs. To quote from the book... 'Ralph, carried away by a sudden thick excitement, grabbed Eric's spear and Jabbed at Robert with it.' A little later we are told... 'Ralph too was fighting to get near, to get a handful of that brown, vulnerable flesh. The desire to squeeze and hurt was over-mastering.' Jack grabbed Robert's hair and pulled his head back, then pretended to cut his throat. The game ended with Robert physically hurt, extremely frightened and in tears. He complained that if they were going to kill they needed to use a real pig. "We could use a littlun," suggested Jack and all the boys laughed, assuming he was joking.