think fast

1. verb To be able to think rationally and make shrewd, intelligent decisions on the spot. Things can change in an instant in this industry, so you've got to think fast to be successful. I knew that I had to think fast if I was going to save the girl's life. A good politician must be able to think fast when faced with tricky questions from the press.

2. set phrase An exclamation used as a humorous warning when throwing something to or at someone. A: "Hey, would you mind passing me that orange?" B: "Sure—think fast!" A: "Hey, I didn't mean pass it like a football!"