Yahoo Sports reports: Naomi Osaka was forced to retire from the first grass-court final of her career Saturday, two days before the start of Wimbledon. The four-time Grand Slam champion turned it early in the first set of her match against Czech world No. 11 Karolína Muchová, at the Bad Homburg Open in Germany. Despite playing on after a trainer visit, Osaka lost the set 6-1. After a lengthy game to open the second set — in which Muchová ultimately held serve — Osaka had a brief conversation with her box, including c