Lightly recruited out of high school, Sinnett originally had an offer from Penn before a change in the coaching staff.
He eventually decided to enroll at San Diego at the recommendation from a former Penn coach that he contact the team's offensive coordinator, Tanner Engstrand.
[1][2] He also received preferred walk-ons from Kansas, Harvard, Iowa State, Rhode Island, and Yale.
[9][10] Sinnett signed a contract that included $152,000 in guaranteed money with the Tampa Bay Buccaneers as an undrafted free agent on April 25, 2020.
[12][13] He was waived by the team during final roster cuts on September 5, 2020, and subsequently signed with the practice squad the next day.
[19] On August 31, 2021, Sinnett was waived by the Dolphins and re-signed to the practice squad the next day.
[31] On July 29, 2023, Sinnett signed with the Cincinnati Bengals due to Joe Burrow suffering a calf strain in training camp.
[39] On October 29, 2024, Sinnett signed with the Madrid Bravos of the European League of Football.