My boyfriend did that with a hammer - ouch! Suprisingly, and luckily I guess, he didn't get the kind of painful bleed where they end up having to pierce a hole in your nail to let off the pressure (I had that once, darn windows! Left it for 15 hours and was in so much pain by the end of it I'd have happily let them cut my finger off, never mind a little hole!).
Anyway, it's black as night but the nail doesn't seem to have distorted yet and it's growing out relatively normally.
I've the nail on my right hand playing hockey over 5 years ago: it bent straight away and stayed growing bent, but hopefully it'll be a case off if it keeps growing straight now, it'll stay straight?
Lol x