// Somewhere on top of script
new PoliceCount;
//=============

//Put this under OnGameModeInit

PoliceCount = 0;
//=============

//Under OnPlayerRequestSpawn

if(gTeam[playerid] == TEAM_POLICE)
{
  PoliceCount += 1;
}

//=============

//Under OnPlayerRequestSpawn

if(gTeam[playerid] == TEAM_POLICE && PoliceCount >= 5)
{
  SendClientMessage(playerid,COLOR_RED,"There are already 5 police officers, choose another team!");
  return 0;
}

//==================

//Put this under OnPlayerDisconnect
if(gTeam[playerid] == TEAM_POLICE)
{
  PoliceCount -= 1;
}