Definition of throw (or knock) someone for a loop in US English:

throw (or knock) someone for a loop

phrase

North American
informal
  • Surprise or astonish someone; catch someone off guard.

    • ‘I think I threw her for a loop when I said, ‘That's fine, honey.’’
    • ‘There's only one aspect of the DVD that doesn't satisfy, and while it's not quite enough to ruin the disc for me, it certainly threw me for a loop.’
    • ‘I can't dictate those parameters and that throws me for a loop.’
    • ‘I suppose it's amusing that I have no problems using a mouse or trackball, but this ‘natural’ pen interface is throwing me for a loop because it's not a direct interface.’
    • ‘It's a powerful connection that can really throw you for a loop.’
    • ‘He was a grown man with enough experience to fill up a book where women were concerned, but this slip of a girl had somehow managed to throw him for a loop.’
    • ‘He had expected everything to go well between Keira and Adam, and this fight threw him for a loop.’
    • ‘I wasn't too sure if I was supposed to be convinced, or if it was supposed to throw me for a loop.’
    • ‘The two people who are supposed to love you the most - love you no matter what - left me and it really did knock me for a loop.’
    • ‘But the fact that people want to shop that way on the Web sort of threw us for a loop.’