I have seen players who are on their smurf accounts adding enemies as friends, and joining the enemy's party to give friendly intel in an effort to throw. Smurfs do this to de-rank and it saves them from having to throw openly, and they often do not get reported.

I played a game today where our Sova asked the enemy Sage to add him because he is going to throw. Then every round he would bait team-mates, remain immobile in a corner, and start moving as soon as I spectate him. It was quite clear he was giving the enemy our positions as the enemies would pre-fire in clutch situations.

IMHO, adding enemy as friends, or joining the enemy player's party, should not be allowed while a game is in progression. People can add the enemy players, of-course, after the game has concluded.