It was the first multi-car accident of the race, after about 157 laps of racing. #6 Ryan Briscoe and #99 Townsend Bell brushed tires, and ended up in the wall, putting them both out for the day. It looks from the replay like Bell drifted too far to the left going into turn #1, and Briscoe buzzed Bell's back left tire and left side pod with his own right front tire. This made Briscoe lose control, and he put both of them in the wall. And THIS is why IndyCar beats the hell out of NASCAR, also called the Taxi Cab Circuit.