C.M. Punk was originally offered the starring role and he was interested in it. According to Punk, during negotiations, Randy Orton was cast without Punk's knowledge.
In the beginning of the movie when Nick and his wife witness the traffic collision, both cars area seen skidding to a stop on their wheels. In the next scene after Nick has his wife get his medical bag, both cars are upside down and on fire.
When Nick is beating Tommy in the hotel room, the phone rings. In a close-up, the telephone is straight on the table but in the next shot it has moved and there is a wire over it which was not there before.
When Heller first calls Nick in the ambulance, Nick is wearing gloves. When we see the closeup of the phone, the gloves are gone. When the camera goes back to showing Nick, the gloves are back.