[Nero_3D]

pawn Code:

new Players;

pawn Code:

//OnPlayerConnect
Players++;

pawn Code:

//OnPlayerDisconnect
Players--;

pawn Code:

//OnPlayerRequestSpawn
new tmembers = -1;
#define NUM_TEAMS (11)
for(new i; i != MAX_PLAYERS; i++) if(gTeam[playerid] == gTeam[i]) tmembers++;
if(tmembers >= floatround((Players / NUM_TEAMS), floatround_ceil))
    return !SendClientMessage(playerid 0xFFFFFFAA, "Please choose another team!");

That would be an easy example of a team balancer, it stops the player from spawning if the team is at his maximum size
The maximum size is Players divided through team count