John is without question, a tennis phenomenon, one of the greatest players the world has ever seen. He held the number 1 world ranking in singles between 1980 and 85 for no less than 170 weeks. He won 17 Grand Slams, 7 in singles (4 US Open tiles and 3 Wimbledon titles) and is also probably the greatest doubles player ever, with 9 Grand Slam doubles titles to his name and 1 in mixed doubles (French Open). He is the greatest Davis Cup player in history. Add to that a string of Emmys for his tennis commentary and we can safely conclude if anyone is qualified to teach, he is.