What about, if you hit an enemy while running and having good speed, it would give a critical or at least buffed attack?
So I thought of this, what about, if you have been running for at least four tiles in a direction, without changing direction, and with a good speed of course (so it wouldn't work while you are too hurt), you'd gain "momentum". A message would appear to indicate it, of course.
Momentum would do two things, it would make the next melee attack buffed, and it would also hamper the ability to aim.
Therefore buffing and nerfing.
It would make moving and attacking a bit more interesting than just "attack and back away, preferably to bushes". It helps people who have an aggressive way of playing.
Of course, of you walk one tile or move in another direction, momentum is lost.