After setting what was then the top average speed of 108.658 mph early in the 55-minute session, Kyle Busch went off course in Turn 11, spun and hit in the inside retaining wall, doing significant damage to his No. 18 Toyota.
The incident took place about 26 minutes into the session.
Busch’s team had to move to a backup car and he will also have to start Sunday’s race from the rear of the field, regardless of where he qualifies on Sunday morning. Sunday’s Cup race will be the first at Road America since 1956.
Meanwhile, in the final minutes of practice, Kurt Busch rocked to the top of the speed chart with an average lap speed of 108.874 mph, on the final of his nine laps in practice.
Kyle Busch ended up second, Austin Cindric was third (108.525 mph), Ryan Blaney was fourth and Tyler Reddick rounded out the top-five.
Completing the top-10 average speeds were Denny Hamlin, A.J. Allmendinger, Christopher Bell, Kyle Larson, and Chase Briscoe.
About seven minutes into the session, Ryan Preece went way off course in Turn 11, doing significant damage to the front of his No. 37 Chevrolet. The team decided to go to a backup car and he will also start Sunday’s race from the rear of the field.
“That’s probably the best road course car I’ve had for a half a lap,” Preece said. “Not the way I wanted to start the day. Hopefully we can go rebound tomorrow.”
About 15 minutes in, Kyle Tilley, driving the No. 78, went spun off in Turn 1 and ended up stuck in the gravel pit to bring out a caution.
About 40 mins in, Brad Keselowski spun off Turn 11 to bring out a caution. He was able to continue on and take his No. 2 Ford back to pit road. He did not appear to suffer any significant damage.