Ammount of Players

how can i check the ammount of players on a team?

my reason:
i want to make a team-balance

[lua]
(button pressed)
if Team_1 > team_2 and team_1.Selected
then
HUD.PrintCenter (Team 1 is is too full!)
return false end
elseif team_2 > team_1 and team_2.selected
then
HUD.PrintCenter (Team 2 is is too full!)
return false end
[/lua]
code is giberrish, but should get the idea out