[2][1] He played for YMS Celtics, FC Delco Academy along with the Montgomery Maniacs as a young man in Pennsylvania before spending a semester at the U-17 national team residency at IMG in 2010.

[3][4] After retiring from soccer in 2016 at 21 years of age, as of January 2017, he was a junior at the Fox School of Business and Management department of Temple University; he became an investment banker thereafter.

[9][7] He was the fourth-youngest player ever to sign an MLS contract, behind Freddy Adu, Fuad Ibrahim, and Diego Fagundez.

[10] He made his regular season Philadelphia Union debut on September 17 against Columbus Crew, at 16 years of age.

Pfeffer was traded to the Colorado Rapids in January 2016 in exchange for the overall second pick in the 2016 MLS SuperDraft, which was used to draft defender Josh Yaro.

"[2] Pfeffer represented the United States at the U-14 and U-15 levels and trained at the IMG Academy in Bradenton, Florida, as part of U.S. Soccer's U-17 residency program.