knock for a loop

Related to knock for a loop: get off the ground, give it a shot, cut some slack

knock (one) for a loop

To shock, surprise, astonish, or bewilder one, especially in a distressing or upsetting manner. I know the death of his mother really knocked Tom for a loop. It knocked everyone in the company for a loop when Olivia announced that she was leaving.
See also: knock, loop
Farlex Dictionary of Idioms.

knock someone for a loop

 
1. Fig. to strike someone hard. You really knocked me for a loop. I hope that was an accident. DI was really knocked for a loop by the falling branch.
2. and throw someone for a loop Fig. to confuse or shock someone. (This is more severe and upsetting than throw someone a curve.) When Bill heard the news, it threw him for a loop. The manager knocked Bob for a loop by firing him on the spot.
See also: knock, loop
McGraw-Hill Dictionary of American Idioms and Phrasal Verbs.

knock for a loop

Also, throw for a loop; knock down or over with a feather ; knock sideways. Overcome with surprise or astonishment, as in The news of his death knocked me for a loop, or Being fired without any warning threw me for a loop, or Jane was knocked sideways when she found out she won. The first two of these hyperbolic colloquial usages, dating from the first half of the 1900s, allude to the comic-strip image of a person pushed hard enough to roll over in the shape of a loop. The third hyperbolic term, often put as You could have knocked me down with a feather, intimating that something so light as a feather could knock one down, dates from the early 1800s; the fourth was first recorded in 1925.
See also: knock, loop
The American Heritage® Dictionary of Idioms by Christine Ammer.

knock/throw somebody for a ˈloop

(American English, informal) shock or surprise somebody: The result of the election knocked most people for a loop.
See also: knock, loop, somebody, throw
Farlex Partner Idioms Dictionary
See also:
  • knock (one) for a loop
  • knock/throw somebody for a loop
  • throw (one) for a loop
  • throw someone for a loop
  • surprise (one) by (doing) (something)
  • surprise by
  • you could have knocked me over with a feather
  • knock (someone) over with a feather
  • knock over with a feather
  • knock (someone) down with a feather