
Florian Mayer of Germany returns the ball during the men's singles quarterfinal match against Roger Federer of Switzerland in the Gerry Weber Open 2017 in Halle, Germany, on June 23, 2017. Roger Federer won 2-0. (Xinhua/Joachim Bywaletz)

Florian Mayer of Germany returns the ball during the men's singles quarterfinal match against Roger Federer of Switzerland in the Gerry Weber Open 2017 in Halle, Germany, on June 23, 2017. Roger Federer won 2-0. (Xinhua/Joachim Bywaletz)