Four years of football are calculated to breed in the average man more of the ingredients of success in life than almost any academic course he takes.

This quote is saying that playing football for four years will help a person be successful in life more than most of the classes that they take in school. Football teaches important skills and qualities such as teamwork, discipline, communication, and determination, which are all important for success in life. While classes may teach valuable knowledge and skills, playing football can help a person develop the practical traits that they need to succeed.