Probably depression. Brain injuries are often associated with depression which in turn is associated with suicides.
Bitter fruit. A professional athlete devotes effort into excelling, far beyond what most of us put into anything. The reward may or may not be a pile of money, but a person who senses the brain is damaged cannot enjoy either success, fame or wealth. The damaged mind may be unable to sustain loving relationships, satisfying work, or enjoyable activities. Try to understand ; support efforts to prevent this.