hook.Add( "EntityTakeDamage", "EntityDamageExample", function( target, dmginfo )
    local attacker = dmginfo:GetAttacker()
    if target:IsValid() and attacker:IsPlayer() then
        local actwep = attacker:GetActiveWeapon()
        if IsValid(actwe ) and actwep:GetClass() == "weapon_crowbar" then
            dmginfo:ScaleDamage( 5 )
        end
    end
end)