noun
back of a collar
Refers to the rear part of a collar, such as on a shirt or jacket.
後ろ襟が汚れているよ。
The back of your collar is dirty.
noun
grabbing the back of the opponent's collar (in judo)
Martial arts term, specifically in judo, for gripping the back of the opponent's collar.
後ろ襟を取って技をかける。
Grab the back of the collar and apply a technique.
Compound of 後ろ (ushiro, 'back') and 襟 (eri, 'collar').