I think it would be good to have a Minigame chat basically so your not spamming global with stuff not relevant to everyone else.
Why not use Local */l*?
You do tend to sometimes forget to go into to local before the countdown ends simply because ur either trying to get more people to join or just talking about something else.
having this minigame chat could be turned on automatically when you join the arena. and still have /g [msg] enabled so you can still reply to msgs in global.