public OnPluginStart()
{
    HookEvent("flashbang_detonate", Event_FlashbangDetonate);
}

public Action:Event_FlashbangDetonate(Handle:event, const String:name[], bool:dontBroadcast)
{
    new client = GetClientOfUserId(GetEventInt(event,"userid"));

    if(IsClientInGame(client))
    {
        if(IsPlayerAlive(client))
        {
            GivePlayerItem(client, "weapon_flashbang");
            FakeClientCommandEx(client, "use weapon_knife");
        }
    }

    return Plugin_Continue;
}