trip up
trip up {v.}
1. To make (someone) unsteady on the feet; cause to miss a step, stumble, or fall.
A root tripped Billy up while he was running in the woods, and he fell and hurt his ankle.
2. To cause (someone) to make a mistake.
The teacher asked tricky questions in the test to trip up students who were not alert.
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Source: A Dictionary of American Idioms
