When Gerard confront Kimble in the lab, Kimble says "Here is your man, Gerard," and throws Johnson at him. Johnson pushes Gerard aside with his left arm, then runs into the arms of Simpson. Instead of pushing Simpson aside, as he had Gerard, he grabs Simpson's neck and "hits" Simpson with the stump of his right arm. But as he just has a stump, instead of an arm, he misses Simpson's head by a good 5-6 inches, and this "punch" is clearly not even close to making contact with Simpson's head.
Kimble gets away by crawling into the luggage bay of a bus. The team has already been boarded by the football team, and their luggage stowed in the luggage bay. The bus was clearly ready to leave because as soon as Kimble gets into the luggage bay, it leaves. But if the bus was ready to leave, the luggage bay would have been locked. Otherwise potential thieves could get in and steal property, or the bus could hit a bump and spill luggage out over the highway.