Err... that greatly depends on the profile of the arrow, the angle of impact, and exactly how big the attacker is. I think in many cases you'll find this is not the case. Arrows are built to penetrate, which by definition means they
don't transfer much of their momentum on impact. It's dissipated by friction against internal tissues, converting much of the vector to heat -- and we're only talking about 15 joules or so. Mishaxhi's hammer example is 600
just for the hammer, never mind the momentum of the guy wielding it, and the likelihood that he's in plate armor (which may increase the momentum transfer of the arrow somewhat, but also greatly increases the momentum of the wearer).
And you don't have to hit exactly where you were aiming to do a lot of damage with a sledge.
Point taken, but perhaps you miss the point of what I was saying (don't mean that condescendingly if it appeared that way)
I don't need the arrow to transfer a whole lot of energy, in fact I don't need the arrow to transfer even half the energy it has in ordger to stagger you. If you're running at me full speed and I throw a rock at you that hits center mass,.. sure, your speed may slow by a fraction but you'll still be coming at me close to the same speed. If I throw the same rock, and I hit you on the shoulder with the same force, while I'll conceed you may not fall, your momentum will shift and you'll definately stumble. It's as simple as Newton's laws, If I wanted to stop you I would need to exact the same amount of force that you are producing by charging towards me, if I want to divert you, I only need to apply minimal force to change your trajectory.
You see this in many things.. American football, soccer, kung fu to name a few.
Sure it doesn't take much for a guy with a big hammer to do damage, the reverse is true as well. If I catch said guy with a big hammer in plate mail soon enough, it doesn't take much to divert him either.