Hmm. I think i know what you mean. Some friend of yours joins the enemy team in the lobby and then just afk or feeds your team? I once played with a player named nikitakiller. He attacked creeps in the middle of the enemy towers while a reg was shooting him. I told him to run, i shielded him, i healed him but he died and then he quit. Either he was a retard (not even the worse noob could do that) or a spy, as you said.
Yeah I played (lost) with this same guy. nikitakill. We played Cataract, he took UB, ran straight up the middle, went 1vs2 against another UB and Reg while standing within range of 2 enemy towers. I think he actually set a record for fastest death ever in a game. Then proceeded to feed the opposing team for about 10 minutes before he quit. We actually did better after we got the AI, but still ended up getting waxed.