Sorry, but I have personal experience with my head hitting the ground during a crash. I know if I had not had helmet and had hit my unprotected head on the road as hard as had with the helmet, I would've definitely had a moderate to severe concussion. In fact, when I was 12 I got a new bike and my father took me and the bike to the gas station on base to fill the tires. He let me ride it home and followed to protect me from vehicles. I was going fast down a hill, lost control, and crashed. The rest my father told me. He helped me up and had to support me as I could not walk on my own. My dad took my bike and me home where he gave me a bath to clean me up and was put to bed. I awoke 3 hours later, first memory since just before hitting the pavement, with a bloody pillow began and kept on puking. I ended up in the hospital overnight for a concussion.
My ear doc guarantees that I probably broke one of the small bones in my left ear and the concussion is a big contributor to my severe hearing loss in that ear.