Knockback - why ST not HP?

[Gollum]

Originally Posted by GWJ

Hm you're right, it's resisting that counts. But still, in case of knockback caused by bludgeoning damage, I think nobody resists intentionally (this means charging into attack vactor)

You're right. Resisting knockback is not always (surely never, actually) intentional. It is pure reflexes.

Now, basing knockback on HP rater than ST would mean that your ability to resist knockback would become lower and lower when you are injured. It could make sense ... But what would happen if your HP reach 0 or even a negative score?

Of course, authors could have ruled that it is based on starting HP, but since HP are based on ST and rarely differ a lot, it may just be much simpler to based knockback on ST ...

Just imagine an old and sick elephant with very few HP left. Is his resistance to a mace blow knockback much lower than when he was younger and in full shape? Not really.