Set the scene. Working to get my riding group to draft, speed was 17 mph and I was number two in a four man group. First rider did not have a cycle computer so I called speeds. Lead slowed down as directed, however instead of coasting he applied a bit of brake. I touched his rear wheel and in .5 second was on the ground.
Water bottles ejected 20 yards ahead, Number three man combat rolled over top of my bike and trail rider swerved off into the grass.
Here's the outer helmet damage
The EPS foam cracked through to the inside
I'm from the school of less government and ELECT to wear a bike helmet because I want to. Yesterday I'm glad I did.
I finished up a 50 mile ride and the headache reminded me that if I wasn't wearing a helmet, most likely I would be in the hospital.