William Byron faces a steep championship climb to claim the NASCAR Cup Series title after leaving Darlington Raceway with an engine failure.

Starting 20th, Byron was able to score stage points with ninth in Stage 1 and eighth in Stage 2. Byron was running ninth when he reported a flat tire on the radio. In the middle of the backstretch on lap 316, Byron’s car suddenly snapped left and spun all the way to the middle of Turns 3 and 4. The caution flew. Byron restarted his car and changed four tires, but the issue still persisted.

Under caution, Byron said, “I feel something dragging; something is broken. I can hear it dragging.”

Byron returned to pit road for a second time, but the team could not fix the issue on pit road. He retired to the garage and finished 37th.

“I’ve never had that happen,” Byron said after climbing out of his No. 24 Valvoline Chevrolet. “I felt like I had a flat left-rear tire in [Turns] one and two, so I slowed down quite a bit, and I was going to pit and try to be early on the cycle. I’m not sure; it was super odd. I don’t know if I was blowing up in that process and got oil on my tire or what. We had an eighth- or ninth-place run going, but it was just an unfortunate end to the evening for this No. 24 Valvoline Restore & Protect Chevrolet.”

Byron sits 114 points behind leader Denny Hamlin as the Cup Series heads to the World Wide Technology Raceway for the second round of the Chase.