Knock/throw somebody for a loop Definition 1 of 2Pro Tip 1/3Unexpected Surprise Use this when someone is taken aback by an unforeseen event or information. When I won the lottery, it really knocked my family for a loop. Pro Tip 2/3Emphasized Reaction This phrase adds intensity to the reaction, more than just being surprised. His sudden marriage proposal threw her for a loop. Pro Tip 3/3Casual Expression Best used in informal situations like conversations with friends. Hearing her sing for the first time knocked us for a loop.