People dealing drugs in your yard is a threat to you.
That's a valid point. I'm not a big fan of undercover cops. They should be in uniform or conspicuously display a badge while on duty. I can certainly see going out to confront what you expect are drug dealers, and they tell you to drop their gun. Even if they said they were police, (I don't think the story said they identified themselves though.) once a situation escalates to pointing weapons, there is a good chance someone is going to get shot.