DARLINGTON, SC - SEPTEMBER 04: NASCAR Hall of Famers Darrell Waltrip and Mark Martin speak in a press conference during the NASCAR Sprint Cup Series Bojangles' Southern 500 at Darlington Raceway on September 4, 2016 in Darlington, South Carolina. (Photo by Blaine Ohigashi/Getty Images)

DARLINGTON, SC - SEPTEMBER 04: NASCAR Hall of Famers Darrell Waltrip and Mark Martin speak in a press conference during the NASCAR Sprint Cup Series Bojangles' Southern 500 at Darlington Raceway on September 4, 2016 in Darlington, South Carolina. (Photo by Blaine Ohigashi/Getty Images)

DARLINGTON, SC - SEPTEMBER 04: Actor and Bojangles' Southern 500 National Anthem Performer, Barry Williams, speaks to the media prior to the NASCAR Sprint Cup Series Bojangles' Southern 500 at Darlington Raceway on September 4, 2016 in Darlington, South Carolina. (Photo by Josh Hedges/Getty Images)

DARLINGTON, SC - SEPTEMBER 04: Actor and Bojangles' Southern 500 National Anthem Performer, Barry Williams, speaks to the media prior to the NASCAR Sprint Cup Series Bojangles' Southern 500 at Darlington Raceway on September 4, 2016 in Darlington, South Carolina. (Photo by Josh Hedges/Getty Images)

DARLINGTON, SC - SEPTEMBER 04: Actor and Bojangles' Southern 500 National Anthem Performer, Barry Williams, speaks to the media prior to the NASCAR Sprint Cup Series Bojangles' Southern 500 at Darlington Raceway on September 4, 2016 in Darlington, South Carolina. (Photo by Josh Hedges/Getty Images)

DARLINGTON, SC - SEPTEMBER 04: Dr. Micky Collins of the University of Pittsburgh Medical Center Sports Medicine Concussion Program, speaks during a press conference with Dale Earnhardt Jr. prior to the NASCAR Sprint Cup Series Bojangles' Southern 500 at Darlington Raceway on September 4, 2016 in Darlington, South Carolina. (Photo by Blaine Ohigashi/Getty Images)

DARLINGTON, SC - SEPTEMBER 04: Dale Earnhardt Jr. speaks to the media prior to the NASCAR Sprint Cup Series Bojangles' Southern 500 at Darlington Raceway on September 4, 2016 in Darlington, South Carolina. (Photo by Blaine Ohigashi/Getty Images)

DARLINGTON, SC - SEPTEMBER 04: Dale Earnhardt Jr. listens as Dr. Micky Collins of the University of Pittsburgh Medical Center Sports Medicine Concussion Program, speaks during a press conference prior to the NASCAR Sprint Cup Series Bojangles' Southern 500 at Darlington Raceway on September 4, 2016 in Darlington, South Carolina. (Photo by Blaine Ohigashi/Getty Images)