Catch (one) on the hop British informal verb phrase
To do something when someone is not expecting it and is not prepared for it.
To be honest, I didn't think you would finish it so quickly. You really caught me on the hop.
Poor Jake! Jane's turning him down really caught him on the hop.
Someone or something that tends to be unpredictable
To say something without thinking
Used to express surprise
To be the worst of all the bad things that have happened.
If a story, event, or announcement has a sting in its/the tail, it seems pleasant at first but contains a surprising and unpleasant part at the end.
The verb "catch" should be conjugated according to its tense.