Revealing mistake: In the scene at the beginning, when Vin Diesel has rescued the professor and has gone into the helicopter to find the pilot dead, he walks back through the door to call the professor, and gets shot. He slides down and you see a bullet hole in the door. Yet before he gets shot, as he starts to walk through the door to call the professor, the bullet hole is already in the door. (00:05:40)
Revealing mistake: When Shane is fighting the two ninjas, they are armed with expandable batons, which are tubular hardened steel. During the fight sequences you can see the plastic batons bending repeatedly.
Answer: No, it is just his sock.
It's a cast with a sock over it. Since the movie is shot out of sequence, possibly he might have hurt it during production.