Complex sentence: Sizemore was supposed to enter the Cadillac Escalade and stay there until the scene ended, the stunt coordinator told him not to pull out, he pulled out regardless not realizing that the stuntman was in front of him.
Split into simpler sentences: Sizemore was supposed to enter the Cadillac Escalade and stay there until the scene ended. The stunt coordinator told him not to pull out, but he pulled out regardless not realizing that the stuntman was in front of him.