pleas explain

why can a smurff a d3 smruff play in a low tier rank game im silver trying to hit gold before the season ends but im finding it very hard due to smruffs and premade teams i would like to know how a game that prides its self on being competitive can allow people to smurff and ruin peoples games its not cool seeing a top lane darius diamond smurff running around with 8 kills in 10 min not only that but i just got promoted to silver 1 and now i have lost 2 games in a row not happy with the way riot is allowing this to happen in alot of competitive games your account will be banned for smruffing and you people act like its no big deal allowing people to ruin ranked games if they cant win in there won teir maybe they should quit not go in some silevr persons game and mess it up