Question: what happened to hiccup's leg in how to train your dragon?
Answer: In "The Zippleback Experience", Hiccup's leg was damaged multiple times. His leg was damaged while Toothless was carrying Barf and Belch to safety, forcing him to use a spare that was later bent out of shape when the grateful Barf and Belch crash into him (Prompting the twins to joke that Hiccup is on his "last leg").