Complex sentence: Grace manages to knock of Korshunov weapon, so Marshall would have the chance to wrestle with Korshunov, eventually forcing his chute to open, wrapped a rope around Korshunov's neck and pulling him out of the plane and killing him.
Split into simpler sentences: Grace manages to cause Korshunov to lose hold of his weapon, so Marshall would have the chance to wrestle with Korshunov. While he is fighting, he wraps a rope around Korshunov's neck and forces his chute to open, pulling him out of the plane and killing him.