When two men place TJ in his wheelchair after he does burnouts in his reverse trike, TJ's right foot is not in the footrest. He moves his foot into the footrest on his own, which would be impossible if he were paralyzed from the waist down.
In the scene where Smoke and Kid are talking after the drag racing scene where Kid crashes, a race track worker can be seen in the background sweeping up. The track worker is making a sweeping motion with his broom but the broom is clearly not touching the ground.
As Smoke is running up to where Kid wiped out during his race with Dogg, Kids' bike is laying on it's side about 30 feet past him in the middle of the track. But in the next shot as Smoke reaches Kid, the bike is only a few feet away from him, up against the track wall and smoking badly.
No tattoo artist in their right mind would have a client stand freely, especially in such an awkward position, as the girl getting her boyfriend's name is. The body is likely to move or jerk. Securing the body against the back of a seat or lying down.
At the end of the final race between Smoke and Kid, the motorcycles are presumably going very fast. Given that the finish line as an overhanging sign at a T-intersection, there is no way the bikes would be able to slow down fast enough to avoid collision with the fence once crossing the line, especially on a dirt road with street tires.
When Kid is playing a video game with his little brother, Will Jr. is using both trigger buttons on each side of the controller, mashing them wildly with two fingers on either side. However, when Anita sits down to play, she doesn't use them at all.