The Gamesters of Triskelion - S2-E16
Continuity mistake: During the final match, while Kirk fights the lone Andorian thrall two things to notice. Kirk's collar of obedience opens up and drops between the two opponents, then when Kirk lifts and flips the Andorian thrall the back of Kirk's black pants are split open in the wide shot. Both the collar and pants are intact in following shots. (00:45:25)