PRO TENNIS: Serena Williams says 'countdown has begun' to retirement

Serena Williams holds her trophy after defeating her sister Venus during the women's singles final at the Australian Open on Jan. 28, 2017, in Melbourne, Australia. (AP FILE)
Serena Williams holds her trophy after defeating her sister Venus during the women's singles final at the Australian Open on Jan. 28, 2017, in Melbourne, Australia. (AP FILE)

Saying “the countdown has begun,” 23-time Grand Slam champion Serena Williams announced Tuesday she is ready to step away from tennis so she can turn her focus to having another child and her business…