[1] Knapp won the State Championship in 2005 with McQuaid Jesuit High School, which he attended for his freshman and sophomore year.

On April 3, 2012, Knapp signed a two-year entry-level contract with the Buffalo Sabres of the National Hockey League (NHL)[2] and was assigned to their AHL affiliate, the Rochester Americans.

On April 12, 2014, Knapp made his NHL debut when he entered the Buffalo Sabres' net, in relief of the injured Matt Hackett, with 11:35 remaining in a 4–1 loss to the Boston Bruins.

Knapp was designated a restricted free agent, but was not tendered an offer by the Buffalo Sabers prior to the 2014–15 season.

[5] On August 6, 2014, as an unrestricted free agent, he signed a one-year AHL contract with the Lehigh Valley Phantoms.