Trump tweeted a video of Holtz giving his endorsement:
"The main reason I'm endorsing him -- I've played his golf course, I've stayed in his hotel, he does nothing but go first class in everything," Holtz said. "He wants his country to be first class as well."
Holtz, who led Notre Dame to a national championship in 1988, gave his endorsement the day before the Indiana primary elections. Another sports legend, former Indiana University basketball coach Bobby Knight, appeared at a Trump rally last week.