During his last placement match for Season 13 of Overwatch competitive play, streamer Tony Macaroni left his last placement match, then rejoined and discovered he had been placed.
After winning the first round of Control on Nepal, Macaroni leaves the match after wishing his team good luck in the rest of their placements, then rejoins seconds later.
When he gets back into his previous game the streamer seems a bit confused, but not as confused as his team.
"Alright, I'm back?" Macaroni asks his team. "Dude were you GM this whole time?" one of his confused teammates replies.
"Wait what the fuck it placed me!" the streamer laughs. "New hack boys, if you want to see your placements, you just leave in your last game and you get placed."
The fact that he left the game probably meant Tony got placed on a loss, and even if he ended the match he was in with a win, he wouldn't gain any SR from it because he had left the match.
It seems to be just an exploit of the way competitive matches work, so it's unknown if this "strategy" is a glitch or not, or whether Blizzard is going to do anything to fix it.