CODINGHIRUJA

Hello. I'm creating a multiplayer chess game. Now i'm still developing the game pairing section. Now I want to show which players are online.
Like these players are online.

1.Griffpatch
2.Hiruja
3.Beluga
4.JohnDoe

Then someone starts a game. So then the script chooses pick random 1-4 and select Hiruja. Then the game continue as the rest.

What I have done is, when you click the green flag. It adds your name to active players list (it's a cloud list) then pairs you with others, The problem I have is
when you leave the game, how can I know you left and remove your name from the active players list?

Please help!!! Very urgent.

Thanks