[miokie]

At The top of the script

pawn Код:

new TeamPM;

OnGameModeInit

pawn Код:

TeamPM = 0;

Where you assign the team

pawn Код:

if(TeamPM == 0)
{
  TeamPM = 1;
  //ASSIGN THE TEAM HERE.
}
else
{
  SendClientMessage(playerid,Color,"Theres already somebody on that team.");
}

Thats how I would do it.
There is proberly a better way but oh well.