Very interesting and I felt very good chapter for several reasons. One of which was the surfacing of Will's rape damage. I had felt he was being perceived in the story to be dealing with that issue a bit too easily. This chapter showed that the trauma from that was still there, lingering below the surface waiting for something to trigger his real feelings. The violence of Martin, though maybe hard to read, I thought realistically brought that out.
Also I think many if not most teenagers have the thought of running away from home when that get pissed at their parents, though most never follow thru on those thoughts. I think that is just a normal teenage reaction. So Will's running way or wanting to run away would have been normal for a teen his age.
I also thought that as an author Mark did a very good job of making the reader see and feel the multitude of emotions flowing thru Will, changing sometimes at light speed it would seem. From rage to loneliness, anger, purceived hatred, hurt, rejection, revenge etc... The ability to consistantly get one's character's emotions portrayed to the reader where the reader feels those emotions, is one of Mark's writing strong points. That was done well with Will in this chapter.