Complex sentence: In 1900 Heisman, then "the undisputed master of Southern football", was hired by Clemson University; he was the first Clemson coach who had experience coaching at another school.
Split into simpler sentences: In 1900 Heisman, then "the undisputed master of Southern football", was hired by Clemson University. He was the first Clemson coach who had experience coaching at another school.