This well-timed biography of Billie Jean King, who made history both on and off the tennis court, arrives just one day after a two-day series of brilliant tennis finals at the U.S. Open. Watching this profile explains, in part, why tennis has become such a popular TV sport – and especially why, when Serena Williams won the other day, she was given as much prize money as the men’s winner, Rafael Nadal. Check local listings.