kingofnoobia 说:
A sword in my stomach is going to cause exactly the same biological damage than a sword in my back.
No, it really wouldn't. The body isn't symmetrical and any amount of arteries, veins and organs could be pierced either way. If I put a blade through someone from behind and then from the same angle, height, pitch etc. from the front. I guarantee you the biological damage would be totally different.
kingofnoobia 说:
You're on a battlefield, friend. You'll have to do your stab just as quickly as when you were doing it from the front.
If I use what you say and assume that not only are you stabbing them as quickly but with the same impact as from the front you would do more damage from behind. I apologise if what I'm about to say is untrue but from the look of it a lot of people against this idea have it in their minds that because muscle can't stop steel it can't slow it down.
Take a piece of cardboard and put an orange behind it. Get a knife and stab through the cardboard into the orange. Now take a second piece of cardboard and place it and a new piece of card in front of the orange. Stab. There WILL be a difference in the penetration of the orange. Now assume that the card was your muscle when it is relaxed and the orange is say, your kidney. The second piece of card takes into account the tensing of muscles and jarring of body parts when the soldier sees a strike coming (hell that's what flinching is for, bracing).
This is of course, not taking into account the armour and differences in thickness in front and behind, facings etc.
Now if we assume what you said did NOT include the strength of a swing, the soldier would (likely) strike harder from behind because they have more time (given it may be fractions of a second but still more time none the less). This, consequently, would inflict a greater wound.
I would also like to throw into the arguement that within a battle it would be a rather confusing thing and it would be very rare for a soldier to produce successful blow after blow. The majority of strikes would have been glancing so the damage inflicted would be minimal. Striking from behind gives your opponent no time to dodge, block or parry and would likely result in a successful blow.
Having said all of that. I don't think it would be a viable mechanic to add to MP for many reasons.
1. It would most likely be hard to balance because of the actual values involved with health, calculations based on speed, direction etc.
2. It would probably ruin the experience completely.
The above 2 being the most prevalent to me.