Hartman, who suffered a serious accident at the Asian X-Games, has had a few head traumas in his life. Hartman has decided to stop pushing his luck on the track and call it quits.
Here's a video about Greg Hartman. In the video Hartman talks about his accidents, why he rides, and why he's decided to retire.
Hartman said: "When I was 19 doctors actually told me that I should probably quit riding. But I kept pushing on and thought 'well that won't happen again.' But it did. And then I thought, 'It can't happen a third time.' But it did. Three times is way too much. It wouldn't be right for me to just keep my fingers crossed."