To outwit or outsmart someone by acting against their expectations or plans; to thwart someone’s scheme.
彼は相手の計画を読んで裏をかき、先に契約を取った。
He read the other party’s plan, outwitted them, and secured the contract first.
交渉で相手の裏をかく方法を考えたが、倫理的に問題があると思った。
I thought of ways to outsmart the other side in negotiations, but felt it would be unethical.
将棋で相手の狙いの裏をかいて勝負を決めた。
In shogi I thwarted my opponent’s intended move and decided the game.
To pierce or penetrate through to the other side of something (literal meaning).
釘が板を突き抜けて、裏を掻いてしまった。
The nail went through the board and came out the other side.
ナイフが布を貫いて裏を掻いてしまったので、縫い直す必要がある。
The knife pierced the fabric and came through the back, so it needs to be resewn.