http://www.slate.com/articles/sports/sports_nut/2015/05/indy_500_crashes_james_hinchcliffe_s_indianapolis_500_crash_shows_organizers.html

On Monday during a practice session for Sunday’s Indianapolis 500, IndyCar driver James Hinchcliffe suffered a horrific crash that landed him in surgery for an injured leg. Hinchcliffe’s Honda hit a wall, spun out, and then overturned on its head, before bouncing back onto its wheels. What made Hinchcliffe’s crash unusual was that it was the fourth such crash during practice and qualifying sessions at the Indianapolis Motor Speedway in less than a week. In that period, the thing Indy cars hardly ever do—turn into helicopters on impact with the wall and flip like dollar pancakes—happened four times.