Subungual Hematoma

Bleeding under the nail can be from an acute ( sudden ) incident ( dropping a can on the toe, kicking something ) as seen on the left photo,or can be from chronic irritation ( which is why runners and athletes often lose their nails, due to fit of sand repetitive activities ). The middle and right photos are from repetitive running irritation, not an acute sudden trauma to the site

Treatment will vary depending on the status of the nail, pain, and strength and attachment of the nail