Four-time Grand Slam champion Naomi Osaka earned $55.2 million in the last 12 months, the most by a female athlete in a year, sports business website Sportico reported. She earned $5.2 million from prize money and an estimated $50 million off the court during the 12-month period. Osaka is placed 15th on Sportico's list of the world’s 100 highest-paid athletes.