As a youth, Lappin played in the 2005
Quebec International Pee-Wee Hockey Tournament with the Chicago Mission
minor ice hockey team. Undrafted, Lappin played collegiate hockey with
Brown University of the
ECAC. Upon completing his senior year in the
2015–16 season, with 33 points in just 31 games, Lappin was signed by the New Jersey Devils to a two-year entry-level deal on March 9, 2016. He soon made his professional debut with the Devils AHL affiliate namesake, in Albany, appearing in 12 games for 7 points. In the post-season, Lappin continued his immediate contribution with 5 goals and 7 points in 11 games. In his first full professional season in
2016–17, Lappin made his NHL debut for the Devils on October 28, 2016 against the
Chicago Blackhawks. He recorded his first NHL point with an assist one night later against the
Tampa Bay Lightning. On November 8, 2016, Lappin scored his first NHL goal in a 3–2 win against the
Carolina Hurricanes. On July 1, 2019, Lappin left the Devils organization after 5 seasons to sign as a free agent on a one-year, two-way contract with the
St. Louis Blues for the
2019–20 campaign. Assigned to AHL affiliate, the
San Antonio Rampage, for the duration of his contract with the Blues, Lappin produced just 5 goals and 11 points through 42 regular season games before the season was cancelled due to the
COVID-19 pandemic. As a free agent from the Blues and going un-signed leading into the pandemic delayed
2020–21 season, Lappin was signed to a one-year AHL contract with the Cleveland Monsters, affiliate of the
Columbus Blue Jackets, on January 21, 2021. Lappin remained a free agent with the
2021–22 season underway, before opting to sign a professional try-out contract with the
Lehigh Valley Phantoms of the AHL, affiliate to the
Philadelphia Flyers, on November 23, 2021. Following the conclusion of his contract with the Phantoms, Lappin opted to halt his North American career in agreeing to a contract with Italian based club, HC Bolzano of the ICEHL, on July 22, 2022. ==Career statistics==