public OnPluginStart()
{
    for(new idx = 1; idx <= MaxClients ; idx++)
    {
        if(IsClientInGame(idx))
        {
            SDKHook(idx, SDKHook_WeaponCanUse, OnWeaponDecideUse);
        }
    }
}

public Action:OnWeaponDecideUse(client, weapon)
{
    if(client > 0 && IsClientInGame(client) && IsPlayerAlive(client) && enabled)
    {
        decl String:sClassname[128];
        GetEntityClassname(weapon, sClassname, sizeof(sClassname));
        if(StrContains(sClassname, "knife", false) == -1)
        {
            return Plugin_Handled;
        }
    }
    return Plugin_Continue;
}