on the hop
1. Continually active; very busy; having a hectic or chaotic schedule. I've been on the hop all day long getting various things done. I'm glad to be home now!
2. In a state of unpreparedness; unawares. (Used primarily in the phrases "catch someone on the hop" or "caught on the hop.") If we attack before sunrise, we just might be able to catch our enemies on the hop! I hadn't prepared anything to say at the reception, so I was caught on the hop a bit when they asked me to say a few words.