Its how you tell if hes on your team or not
This is how it works...
If the guy is on your team, the arrow will display over his head no matter were he is in the level. Now, if the guy is on the other team team, he will ONLY show if hes within radar distance, and he will have a red arrow over his head.
Edit - One more thing, in the Team version you can hit your team mates across the level, only so you can test it without killing eachother. Once we release, i'll disable the ability to hit your team mates with melee.