noun
ground technique; pinning technique
In judo, wrestling, and sumo, a technique applied while both opponents are on the ground, such as a hold-down, choke, or joint lock.
彼は寝技が得意で、試合ではよく相手を抑え込む。
He is good at ground techniques and often pins his opponent in matches.
noun
underhanded dealings; dirty trick
Figurative extension from martial arts: a sneaky or behind-the-scenes maneuver, often in politics or business. Carries a negative nuance of unfairness.
政界の寝技にはうんざりだ。
I'm fed up with the underhanded dealings in politics.
あの会社は寝技を使って契約を取ったらしい。
That company apparently used dirty tricks to get the contract.
Compound of 寝 (ne, 'sleep' or 'lying down') and 技 (waza, 'technique'). Originally a martial arts term for ground techniques, later extended figuratively to sneaky tactics.