Men's singles in "real" tennis is the first world championship in any sport. It predates the use of the term "real tennis," as the sport was called just "tennis" until lawn tennis gained popularity. Except in cases where the champion has retired, the championship has always been on a challenge basis — the champion retains the title until losing an official challenge or retiring. Originally, the champion had the right to accept or reject a challenge, usually depending upon the prize money put up by the challenger's sponsor. Several years could thus go by between challenge matches. The top four ranked players in the world (excluding the champion himself) playoff for the right to challenge. The champion and challenger then play a match of up to 13 sets over three days (4 sets, 4 sets and up t