Stamina Conservation
After every wave of opponents that Leo defeated, he staged the same unfortunate accident again and again after the fifth wave, which made the other rankers feel as if ambushing him out of the blue was the best tactic to take him down.
For this, he would purposefully not dodge when an attack came from his blindside and although he could sense it coming, he let it connect, just so that the others felt like they could perhaps do the same.
Mostly, when his opponents noticed that the untouchable 'TheBoss' was not invincible to sneak attacks, they started to go wild with their attacks, taking little regarding for their team-mates, and this helped Leo conserve his stamina big time, as rather than having to kill all 100 opponents by himself, he simply needed to dodge their attacks and watch them kill each other instead, greatly helping him recover his own strength reserves.