We did it for Pathfinder, so let’s do it for DnD!
Distracted Advantage
When they are not looking at you, you spring into action. Gain the following benefits:
- Increase your Strength or Dexterity by 1, to a maximum of 20.
- When you attack an enemy that you have advantage against or an enemy that you and an ally are engaged with, you apply double your ability modifier to damage instead of your normal ability modifier.
Thoughts?
Throat Punch Games 
This would include Barbarians using reckless attack. Seems a bit strong since the “classic” great weapon master barb would also be using that feat and gaining the +10 damage.I know people already complain about GWM and it seems that this would compound the issue.
I don’t think it too much of an issue, as if you hit my bad guy and one hit kill them then you’re my new focus and it’s not too hard to take down a barbarian.