Roger Federer is considered the "Master" of twener, having played some great ones in his career. During an hit with the former world No. 2 Tommy Haas in Stuttgart ahead of the 2016 Mercedes Cup, the 20-time Grand Slam champion hit a tweener on a roof. Roger played the event twice in a row, in 2016 and 2017, respectively losing to Dominic Thiem in the semifinals and Haas himself in the second round last year. Here is the video of the funny moment.