Jon Gruden, Mike Ditka, Dave Osborn, Ahmad Rashad and Joe Horrigan discuss why Bud Grant is one of the greatest coaches in NFL history. (1:24)

Minnesota Vikings Hall of Fame coach Bud Grant checks in at No. 15 on ESPN's countdown of the greatest coaches in NFL history.

From the outside, Grant projected the tough, no-nonsense approach of a classic mid-century football coach. But what has always amazed and often entertained me is the level of psychology Grant employed during his tenure.

In the video, Pro Football Hall of Fame vice president Joe Horrigan said Grant would wear shirtsleeves on the sidelines as mental warfare against opponents. Was he demonstrating how to tough it out during brutal weather conditions? Was he telling the other team that he and his players were better adapted to the cold? Opponents were left to decide.

Former player Ahmad Rashad noted Grant's theory on illness: You played better when you were sick because your focus was narrowed. And this 1976 article provides a rundown of Grant's use of humor to motivate. When a particularly deep-sleeping team employee began snoring next to the pool at a team hotel, Grant dumped a wastebasket of ice water on him -- defying team officials who said the employee couldn't be woken up. "Nothing's impossible," the article quotes Grant as saying.

That was Bud Grant, as much as four Super Bowl appearances.