I did that to someone at a night game once, it was too dark to tell what team he was on and I'd just knowingly walked right into the enemy base and not been shot.
So I started wondering if all the guys walking around were actually on my team and we'd all just swapped positions somehow. Enemy out there, friendly in the base.
So I had to make this guy give up his team colours without making it obvious which side I was on. Took me about 5 minutes to get him to do it, and then I just melee killed him haha. It was one of my finest ever airsoft moments. Sucks it was a night game or I'd have had it on camera.