1. : into a state of amazement, excitement, or confusion
members of the cast were thrown for a loop when they caught sight of him — Cornelia O. Skinner
that strange poetic touch which knocks the Japanese for a loop — Time
2. : into a usually sudden and unexpected reversal of fortune or a state of distress
any such attempt would knock our whole economy for a loop — L.H.Keyserling
Useful english dictionary. 2012.