[eyal282]

Solved!

#include <sourcemod>
#include <sdktools>
#include <cstrike>

public OnPluginStart()
{
	HookEvent("player_team", Event_OnPlayerChangeTeam, EventHookMode_Pre);
}

public Action:Event_OnPlayerChangeTeam(Event:hEvent, const String:name[], bool:dontBroadcast)
{
	hEvent.SetBool("silent", true);
	SetEventBroadcast(hEvent, true); // These two lines are optional to avoid spamming team change messages in chat.
	
	new team = GetEventInt(hEvent, "team");
	
	int client = GetClientOfUserId(hEvent.GetInt("userid"));
	
	if(client == 0)
		return Plugin_Changed;
	
	Event fakeevent = CreateEvent("player_team");
	
	fakeevent.SetInt("userid", GetClientUserId(client));
	fakeevent.FireToClient(client);
	
	CancelCreatedEvent(fakeevent);
    
	if(team == CS_TEAM_SPECTATOR && IsPlayerAlive(client)) // Optional to make spectator team join kill you on the spot.
		ForcePlayerSuicide(client);
		
	return Plugin_Changed;
}