The difference between lions and large theropods is quite substantial. To begin with is size; adult male lions rarely exceed 220kg in weight, with 130kg for females. Even Allosaurus fragilis, one of the smallest brontophagous predators, could have been ten times as large. The square-cube law determines that a certain impact (like, say, falling) would be much more damaging to the theropod than the cat.
Cats also have a fast ''recovery'' system, which so far has not been identified in theropods. They are essentially springtraps (no pun intended); a lioness can recieve a full-on body slam by an adult giraffe and get back on her feet in seconds if it's lucky. ( https://www.youtube.com/watch?v=MX9GrMQoeNc) This situation, when applied