Will my black nail grow back normally? slammed car door on it.

Blood under nail: If you hit your skin very hard, it will damage small blood vessels in your skin, and you will get a bruise, where blood has leaked from the veins into the skin. If you hit your finger nail very hard, you will get bleeding under the nail, which may lift your nail up. There is no where for this blood to go, and the black, old blood, will remain until the nail grows out and it may take months.