What crisis did Mark face? How did Jennings help?

Mark is one of the first people that Jennings meets at the foster home. When Mark is being bullied, Jennings stands up for him and helps to find a more permanent solution than simply ignoring the boy.
At night in the foster home, the adults take the children's toys away, including stuffed animals. The children have to line up to get them back in the morning. As they wait, Butch comes in and starts mocking them for lining up for stuffed animals; he then zeroes in on Mark.
He tells Mark that he can't believe a stuffed animal can fit in bed with him. He mocks him until Mark leaves the line and then mocks him for leaving the line. Other children also leave the line. Jennings decides he's had enough and leaps onto Butch's back, attacking the boy. He knocks him to the floor and hits him several times before Butch gathers himself enough to retaliate; he hits Jennings, and the supervisor finally pulls them apart and smacks them both.
For Butch, Mark is an easy target because he's a chubby, quiet boy with glasses who doesn't stand up for himself. He tries to get through his time in the foster home by keeping his head down and not causing problems. However, this reaction just makes it easy for Butch to keep using him as an emotional punching bag. Jennings stands up for Mark and creates a reason for Butch to stop bullying the boy.
Just before Butch starts mocking Mark again, Mark tells Jennings not to play with him. He tries to put space between them so that they won't care about each other. Despite the unspoken kids' rule that they can't have friends in the home, the boys do end up becoming friends. In a way, this is another crisis that Jennings helps Mark with—he feels like he has no one, and then he has Jennings.
Mark comes to where Jennings is resting with Doggie, Jennings's stuffed animal. He decided not to get his own so he could give Jennings what he wanted. He tells Jennings that maybe it isn't smart, but they're going to be friends.