how does ralph react when a boar comes charging down the path?

I think you are referring to when Ralph finally joins in the hunt. Ralph throws his spear and hits the pig in its snout. Immediately Ralph feels intoxicated with the rush of imposing his will on another living creature. Ralph is elated at both the hunt and being accepted by a group who he has always been at odds with. Ralph joins in on the re-enactment of the hunt on Robert. It is the one time in the novel where Ralph is awash with acceptance and social abandonment.