The guys kept getting hit by his wakeup spinslash, which knocked them backwards. The bullets can be jumped over, only the grenade thing is an issue. But as mentioned, that's a meter burn and the player literally spent the entire meter on doing this. Clash was never used to take advantage of the player's lack of meter, which would have given a lot of health back.
Some of the stuff on that stream was the Harley player trying to outzone Deathstroke. It was clearly not working but the player kept trying it.
