The U.S. Open crowned its winners this weekend. But for a lot of fans, this year’s competition was less about who won, and more about a player who wasn’t even involved in the final matches. Serena Williams, who announced last month that she’d be retiring from tennis after this year’s tournament, has made an indelible impact on her sport and left a legacy away from the court that has very little precedent. Guest: Wesley Morris, a critic at large for The New York Times and co-host of Times podcast “Still Processing.”