I actually think that Mike may have tried to take the gun, not intending to use it, but to keep the cop from arresting and/or shooting him. The cop allegedly yelled "I'm gonna kill you". Whether that was just after the door slamming, or after the punch, is not certain.
Not sure where you're getting that.
If ya try to take a cops weapon, real bad things will follow as the cop will have no idea what your intent is and won't even care at that point.