What Causes Vaginal Bleeding After Being Hit On Lower Abdomen?

i got hit in the lower stomach with a softball really hard & when i ran a little a couple minutes after I walked a little & i could almost not even walk the pain was really sharp , then the pain went away after a little & i noticed when i got home i had blood on my underwear & my menstrual had already finished a week ago & 4 hours hours later i get a little bit of pain what is this ?