If
"Spear Dragon" attacks, even if the damage is reduced to 0 by the effect of
"Waboku" or
"Kuriboh", it is still changed to Defense Position.
"Spear Dragon" will change to Defense Position after it attacks, regardless of the battle position of the opponent’s monster.
The effect of
"Spear Dragon" does not prevent you from manually changing its battle position later on. Of course, you cannot change it in the same turn after you attacked with
"Spear Dragon". But during your next turn you can change it back to Attack Position (and attack again the same turn, if you choose).
If you attack your opponent’s Defense Position monster with 0 DEF with your
"Spear Dragon", and have
"Dragon’s Rage" active on the field, the opponent only takes 1900 points of damage. The effects are not cumulative.
The effect of
"Lord of D." will not prevent the effect of
"Spear Dragon" from changing it to Defense Position after it attacks.