The Yokohama BayStars selected Yamaguchi with the first round in the. He began his professional career with the Yokohama BayStars in 2006. He played for Yokohama from 2006 through 2016. He signed as a free agent with the Yomiuri Giants in 2017. In 2019, he posted a 15–4 record that led Japan's Central League, along with a 2.91 ERA and 188 strikeouts over 170 innings. After the season, on October 1, 2019, he was selected for the Japan national baseball team at the 2019 WBSC Premier12. After the 2019 WBSC Premier12, on November 18, 2019, Giants held a press conference announcing the team has allowed Yamaguchi to enter the posting system to play in Major League Baseball. Paperwork for the posting was completed on December 3, 2019 and Yamaguchi became the first player in Giants history to be posted.
Major League Baseball
On December 28, 2019, Yamaguchi signed a two-year, $6.35 million contract with the Toronto Blue Jays and will wear uniform # 1, being only the fourth Toronto pitcher to ever wear a single digit uniform number. On January 15, 2020, He held a press conference in Toronto. After the press conference, he stayed in Toronto, and attended a fan meeting. On March 26, he returned to Japan due to the COVID-19 pandemic. He returned to Toronto after the MLB announcement of the 2020 regular season. On July 27, 2020, Yamaguchi made his MLB debut. He became the first Japanese player who made his MLB debut as a Blue Jays member.
Playing style
Yamaguchi is a 6 ft 2 in, 225 lb right-handed pitcher. He throws a fastball averaging 90 mph as a starter. The forkball is his primary secondary pitch and he also has a slider.
Personal life
His father is Yamaguchi Hisashi, a former champion sumo wrestler. On December 25, 2014, Yamaguchi married Japanese gravure idol and :ja:高木加織|Kaori Takagi. The marriage was only announced on March 14, 2015 by Takagi in her official blog and less than a week later, their daughter was born on March 20, 2015. Takagi gave birth to their second child, a son, on August 20, 2016. Yamaguchi was suspended for the second half of the 2017 season, after being charged with causing bodily harm to a hospital security guard as well as heavy damage to hospital property, while intoxicated. He reportedly was at the hospital to receive treatment on his pitching hand.
