Repetitive, sub-concussive impacts (i.e. impacts that do not produce overt signs or symptoms) cause damage to the brain when experienced repeatedly, and research suggests that these lead to neurodegeneration later in life.
So, with little pain, and no obvious physical injury, brain trauma in sport really is a serious injury that is “hidden in plain sight”. This is very different from other more visible and painful injuries in sport e.g. knee, ankle and shoulder injuries.