Can I say "have to flip" instead of "have to do a flip"? It seems like the verb "flip" already have the meaning of "do a flip". Which one is more common?
You are correct that you can say "have to flip" instead of "have to do a flip". Because, as you said, "flip" is already a verb. Both phrases in this context, however, are correct and equally common. Ex: He always flips over onto his back. Ex: She wanted to do a flip, but it's too dangerous.