啥算轻伤啊。

他这种没有脑水肿，脑震荡？

顺便说下，自行车头盔不保护脑震荡（concussion）"While helmets don’t protect against concussions, they have consistently proven to reduce severe head injury and death for cyclists."

https://www.discovermagazine.com/health/the-science-behind-bicycle-helmets-protecting-cyclists