Petersen was born in London to a white American father and Nigerian mother.[1][2][3] At age one, Petersen moved to California, his father's home state.[2] Petersen grew up in San Jose and attended Saint Francis High School.[4]
After one year at West Valley, Petersen transferred to Riverside City College, playing one game in the 2014 season, for 1+1⁄3 innings pitched, two strikeouts, and no runs allowed.[6]
Petersen signed a minor league contract with the Los Angeles Dodgers on January 24, 2024 and began the season with the Triple-A Oklahoma City Baseball Club.[7] On June 16, Petersen was selected to the 40-man roster and promoted to the major leagues for the first time.[10] He made his MLB debut two days later against the Rockies, allowing one run on one hit and one walk while striking out two in two innings to pick up the win. His first strikeout was of Elehuris Montero.[11] He pitched 14 innings over 11 games for the Dodgers, with three wins, a 6.43 ERA, and 11 strikeouts.[12] Petersen also appeared in 35 games for Oklahoma City, with a 1.64 ERA, 10 saves, and 44 strikeouts.[5] He was designated for assignment by the Dodgers on September 8.[13]
Miami Marlins
On September 10, 2024, Petersen was claimed off waivers by the Miami Marlins.[14] In 5 appearances for the Marlins, Petersen logged a 4.76 ERA with 3 strikeouts across 5+2⁄3 innings pitched.