What is demanded by the gunman in the flashback in Chapter 47? How is the gunman overpowered?

The man with the gun, who has just shot Baxter, yells at everyone to shut up. He demands food and fuel. The others obey, bringing fuel from the generators and food from the snack machines. Suddenly, Alec makes his move, swatting the gun away from the man. He and Mark then tackle the man, while Lana chases down the female.