From 2006 to 2009 he was a student assistant football coach at Cortland. His duties included video operations, assisting with the offensive line and quality control.[2] In the 2010 spring season, he worked briefly with the Cortland offensive line, before moving on to Syracuse.[3]
Rothstein interned with Syracuse's video operations department during the fall of 2009.[1] Rothstein spent two seasons at Syracuse, 2010–2011, as an offensive quality control coach.[4]
He joined the Lions in 2012 as a quality control/special team coach and had responsibility for breaking down film of opponents. Rothstein was offensive assistant coach from 2015–2017.[5] In 2018, under coach Matt Patricia, he became "head coach assistant/research & analyst," mainly focusing on defense.[6] In December 2020, because of quarantine restrictions, he became the defensive play caller for a game against Tom Brady.[3]
Rothstein moved to the Patriots in 2021, with Matt Patricia.[7] He started as a member of the research and analysis department.[8] He moved up to offensive assistant in 2022 and in 2023 became assistant quarterback coach. In the 2024 move to a new head coach, Rothstein was retained and given a new role, assisting head coach Jerod Mayo in situational matters; there was no official name designated for this position.[9] His role appears to have been similar to that of former Patriot research director, Ernie Adams.[10][11]
On March 6, 2025, Rothstein was hired by the Denver Broncos as their director of game management and offensive line assistant.[12] Ahead of the 2026 season, Rothstein was named the assistant quarterbacks coach in addition to his duties as director of game management.[13]