I think that tennis may be the most mentally demanding sport there is (high on the list with Golf), and it is one of the most physically challenging too. It isn't physically challenging in the sense that your body is constantly being banged around like in a contact sport, but the agility, endurance, and stamina it takes to play tennis is astounding. Trust me, I play. If you only could participate at a higher level of tennis at say, your local club or your high school, and you competed, only then would you be able to understand why tennis is an amazing sport to play AND to watch. Before I played in high school I never really liked watching tennis on tv, but now that I'm competitive and serious about it, I absolutely love watching it on tv.