I have been trail riding for 30 years, and frequently go on group rides. I don't always wear a helmet, but for some reason I decided to wear one on Wednesday.
My horse is not as experienced as he should be for his age (he is 14) since he spent the first 11 years in an arena as a reining horse. I ride him several times a week, and try to get on the trail as much as possible to boost his confidence. He gets scared and resists when pushed to something he is not sure about.
I was on a trail ride with 25 friends and when he did not want to cross a ravine, I pushed him to cross and he resisted into a full rear up! I could not grab the reins to pull his head down and felt my best chance was to roll off and avoid being landed on.
When I went off, I landed with my head on a rock! I escaped with a only a bruised ego, and it is only because I was wearing a helmet.