Any ally that is running directly towards you and is at full health is probably a spy. A newbie spy. Set him on fire, or jarate him, and watch him flail around like a lunatic with the knife once his cover's blown.
It's important to remember that spies are harmless when invisible. They can't attack until they decloak, so you don't have to worry about being killed by an invisible guy. Just watch for strangeness on your own team. If you see the same guy walk past a doorway twice in three seconds, it's not a glitch in the Matrix, it means one of them's a spy. If you see a front-line class like soldier or scout hiding in a corner somewhere, shoot him to be sure.
If you encounter a spy in the field, remember to constantly face him. Always backpedal, don't run past him, because then his knife has a clear opening to your immensely vulnerable spine. And finally, don't underestimate the revolver. It's the third most accurate weapon in the game after the sniper rifle and rocket launcher, and three or four hits will kill most classes. Don't stand there firing and let yourself get hit.
Keep moving, keep him in your sights, engage him at range, and watch the bullets.
It's important to remember that spies are harmless when invisible. They can't attack until they decloak, so you don't have to worry about being killed by an invisible guy. Just watch for strangeness on your own team. If you see the same guy walk past a doorway twice in three seconds, it's not a glitch in the Matrix, it means one of them's a spy. If you see a front-line class like soldier or scout hiding in a corner somewhere, shoot him to be sure.
If you encounter a spy in the field, remember to constantly face him. Always backpedal, don't run past him, because then his knife has a clear opening to your immensely vulnerable spine. And finally, don't underestimate the revolver. It's the third most accurate weapon in the game after the sniper rifle and rocket launcher, and three or four hits will kill most classes. Don't stand there firing and let yourself get hit.
Keep moving, keep him in your sights, engage him at range, and watch the bullets.