敵てきに付つく

expression, godan verb (-ku)

side with the enemy; join the enemy's side

Used when someone switches allegiance to the opposing side, often in a conflict or competition.

• 彼かれは裏うら切ぎって敵てきに付ついた。

  He betrayed us and sided with the enemy.

• 戦せん争そう中ちゅうに敵てきに付つく者ものは処しょ罰ばつされる。

  Those who side with the enemy during war are punished.