A girl can bleed if a guy goes too deep as deep penetration of the vagina can cause minor amounts of bleeding if it happens to bruise the girls cervix.
When a girl bleeds when the guy goes too deep during sexual intercourse it is called postoital bleeding and is fairly common and affects around 9 percent of women that are of age to reproduce.
Most bruised cervix's heal within a few days and have no long term complications.
Other causes of bleeding after sex include uterine fibroids or endometriosis, hormonal changes like breastfeeding, pregnancy, menopause, infections and rarely ovarian cancer or cervical cancer.
An Orgasm or sexual intercourse can also cause some light bleeding in the first trimester of pregnancy.
During the first trimester of pregnancy your cervix is more sensitive and receives more blood flow, which can cause bleeding or spotting after sex.
This is not usually a cause for any concern and is normal.
A small blood filled area in the uterus called sub chorionic hemorrhage can cause bleeding during the first trimester and during pregnancy and is not often a cause for a miscarriage.
Spotting can also occur when a fertilized egg attaches to the lining of your uterus and usually happens 6 to 12 days after ovulation.
If the bleeding after sex is not painful or is light red, brown, pinkish and short lived, then it is often not a cause for concern.
Orgasm and sex is generally a safe thing to do during pregnancy and can actually have some positive health benefits like reducing stress and also increasing blood flow to your uterus.
Sometimes the act of having sex during pregnancy and during your first trimester can cause enough irritation in the vagina and cause light bleeding or spotting.
Pregnancy hormones can also cause the cells on your cervix to be sensitive to touch and movement, which can result in spotting.
This is a common cause of light spotting in pregnancy and can occur when the cervix is touched during sex, a speculum exam, pelvic exam or even from a pap smear.