Vault key should be context sensitive and the player should:

a) perform a jump if moving

b) vault over something if standing still

c) climb onto something that isnt to high(climbing onto cars or roofs of garden sheds)

d) running into a wall and jumping would cause blood loss/broken bones(legs, arms) if the obstacle is of a certain height

Bonus: kick down doors/running into a door and pressing vault at the right time(also may cause blood loss or broken bones)