Unwieldy Strength (5e Feat)
From D&D Wiki
Prerequisites: Strength 15 or higher, proficiency with martial weapons
You have learned to use unwieldy weapons to more devastating effect.
- When you roll damage for an unwieldy weapon, you add your proficiency modifier to the damage.
- When you critically succeed on an attack with an unwieldy weapon, the target has to make a Strength save vs 10 or 1/2 the damage (whichever is higher). On a failure, they are knocked prone by the force of the blow.