Dropping a loaded gun is dangerous how does the Cop not understand that?

In the pilot episode a cop tells the surrendered bad guy that has his arms up to drop his weapon he doesn't no doubt because it's dangerous so without any freakin good reason responding with anger the Cop slams the car door shut which slamned the bad guy's arm to get the surrendered bad guy to drop his gun before arresting him.

Completely freakin unneccesary and a jerkass inexcusable move.
If that cop gets sued because he caused a injury that was undeniably utterly avoidable I will not feel sorry for him at all.