expression, godan verb (-u)
trip someone up; pull the rug out from under someone
Idiomatic expression meaning to physically trip someone by sweeping their leg, or figuratively to undermine or thwart someone unexpectedly.
See also: 掬う
彼はわざと相手の足をすくって転ばせた。
He deliberately tripped his opponent by sweeping his leg.
With the introduction of the new system, our plan was pulled out from under us.