why i have to drop divisions if there is a brainless dude leaving the match in mid game or from the beggining? do something because that guys destroy the game 
People quitting games is not a support issue, though it is annoying.
There is already a penalty for people who leave games. In addition to losing CSR, the first person to quit will also be subject to a matchmaking cooldown. If someone has left your team already, you can then quit without worrying about a ban, though you will still lose CSR (this is to prevent exploitation).