Complex sentence: After completing the ritual, one of the mob (Lady Gaga) sees Shelby spying on them and the rest of the mob chases Shelby, who flees onto the road and is almost hit by Lee's car.
Split into simpler sentences: After completing the ritual, one of the mob (Lady Gaga) sees Shelby spying on them and rest of the mob gives chase to her. Shelby flees out onto the road, where she is almost hit by Lee's car.