Rafael Nadal doesn’t want to be your average retiree. For most people, retiring with millions in the bank is the kind of dream that ends with a lifetime of lie-ins and leisure. But not Nadal. After over two decades of competing, the Spaniard wrapped up one of the greatest tennis careers in history—22 Grand Slams, a record 14 French Open titles, 209 weeks as world No. 1, and a $220 million net wort...