[Mean]

pawn Код:

new TeamPlayers[ <Amount of teams here> ];

public OnPlayerRequestSpawn(playerid)
{
    for(new teams; teams < [Team Amount]; teams++)
    {
        if(teams == gTeam[playerid]) continue;
        if(TeamPlayers[gTeam[playerid]] > TeamPlayers[teams] + 3)
        {
            SendClientMessage(playerid, COLOR_RED, "You can't join this team as it would unbalance the game!");
            return 0;
        }
    }   
}
//By Hiddos

So... Example usage:

pawn Код:

public OnPlayerRequestSpawn( playerid )
{
    for( new teams; teams < 23; teams++ )
    {
        if( teams == gTeam[ playerid ] ) continue;
        if( TeamPlayers[ gTeam[ playerid ] ] > TeamPlayers[ teams ] + 3)
        {
            SendClientMessage( playerid, COLOR_RED, "You can't join this team as it would unbalance the game!" );
            return 0;
        }
    }
    return 1;
}