Big Knocker: Achievement PSN of South Park: The Fractured But Whole

Most attacks in the game have the ability to knock enemies back. This is almost certainly going to come through natural gameplay.
What you must do is line up two enemies, then use a push attack to knock one enemy into a low-health enemy. This only deals little damage but the knockback damage can be increased with Artifacts later in the game. The enemy who stands at the back has to die from the impact.