Sam had the breath knocked out of him when he hit the tree, but he was not seriously hurt yet. As soon as he was able, he looked around the base of the tree and, fortunately, found his gun. However, no sooner did he find it than did he see Stevie running towards him with the beast fast approaching from behind. It was far faster than either of them, so it seemed hopeless that they would actually be able to get away. 

Sam aimed his pistol, but could not shoot without risking hitting Stevie. After only a few seconds, the beast pounced on top of her, forcing Sam to take the risk. He took the shot, and by sheer luck, it hit the creature square in the head. And yet, somehow, it did not die. It hardly seemed hurt, though it definitely seemed angry. It looked up and growled before rushing at him. He fired two more shots which did nothing before the beast was upon him. It tackled him to the ground and slashed twice across his torso with its massive claws, leading to four massive gashes which immediately started to pour blood. He put his arms up to shield his face, but that did not stop it from clamping down on his forearm with its powerful jaws, ripping through his muscles and crushing the bone. Once it had done sufficient damage, it stopped its attack and turned toward Stevie, stepping on his leg in the process with its full weight, fracturing his femur in the process. Within only the span of a few seconds, it had pounced on her as well. Sam did not know why it has stopped before killing him. Perhaps it did not want Stevie to escape while it was finishing him off? Regardless, he was not going to squander the opportunity to stop that thing from killing her. He grabbed the gun next to him and, through a mixture of adrenaline and sheer willpower, attempted to bring himself up to his feet.