expression, noun
having a guilty secret; having a skeleton in the closet
Idiomatic expression literally meaning 'a wound on the shin'; used when someone has a hidden past misdeed or guilty conscience. Often appears as すねに傷持つ (to have a guilty secret).
彼はすねに傷があるから、警察の話になると急に黙り込む。
He has a guilty secret, so he suddenly goes quiet when the topic of the police comes up.
すねに傷持つ身としては、あまり大きなことは言えない。
As someone with a skeleton in the closet, I can't talk big.
The phrase literally means 'a wound on the shin,' figuratively referring to a hidden flaw or past misdeed that one is ashamed of. The exact origin is uncertain, but it likely draws on the idea of a scar that one keeps covered.