Kossa-Rienzi played youth soccer with Mavericks SC.[1] He attended Berkeley High School, where he was named the WACC-Foothill Player of the Year, the North Coast Section Player of the Year, an All-USA Second Team selection, and an All-American, as a junior.[1][2]
College career
In 2020, Kossa-Rienzi began attending the University of Washington, where he played for the men's soccer team.[2] He recorded an assist in his collegiate debut on February 4, 2021, against the Northwest Eagles.[3] On September 24, 2021, he scored his first collegiate goal in a 2–0 victory over the Portland Pilots.[4] At the end of his sophomore season, he was named an All-Pac 12 Honorable Mention.[5] In 2022, he was named to the All-Pac 12 First Team and the All-Far West Region Second Team.[6][2] Ahead of his senior season, he was named to the Pac-12 All-Preseason Team.[7] At the end of the season, he was named to the All-Pac 12 First Team and the All West Region Second Team.[8] He was also invited to the MLS College Showcase.[9] Over his four seasons, he scored six goals and added 11 assists in 76 appearances.[10]
At the 2024 MLS SuperDraft, Kossa-Rienzi was selected in the first round (23rd overall) by the Seattle Sounders FC.[12][13] After participating in pre-season with the first team,[14] he signed a contract with their second team, Tacoma Defiance, in MLS Next Pro in March 2024.[15][16] During the 2024 season, he went on short-term loans with the Seattle Sounders first team, making his first start on May 22 in a U.S. Open Cup match against Phoenix Rising FC in which he scored his first goal for the club, which was the winning goal in a 2–1 victory to help the club advance to the quarter-finals.[17][18]