expression, godan verb (-u)
trip someone up; pull the rug out from under
Idiomatic expression meaning to catch someone off guard or undermine them, often by exploiting a weakness. Note: This is a common but technically incorrect variant of 足をすくう; the standard form uses 足 (あし) without 元.
See also: 足をすくう (あしをすくう)
彼の質問は私の足元をすくうようなものだった。
His question was like pulling the rug out from under me.
油断していると、足元をすくわれるぞ。
If you let your guard down, you'll be tripped up.