Giving your account to someone to play your placement matches for you
So I played my games at the beginning of the ranked season, went 7/3 or something, got placed in bronze 4. Yet my friend who was the same rank as me last season, went 5/5 and got placed in silver 5. She literally gave her account to a friend to play on and get her to silver 5. She even admitted it. I'm calling bs on the system there.