2014: After starting the year as a reserve, Birnbaum finished the season as an MLS Rookie of the Year finalist, starting in the final 21 games for United after replacing the injured Jeff Parke on June 7 against the Columbus Crew at FedEx Field. The Irvine, Calif., native became the fifth D.C. United rookie of the year finalist in six seasons, joining Chris Pontius (2009 finalist), Andy Najar (2010 Rookie of the Year), Perry Kitchen (2011 finalist) and Nick DeLeon (2012 finalist).
2013: Birnbaum was one of three team captains for Cal. He was a Missouri Athletic Club Herman Trophy Semifinalist, named a NSCAA First Team All-American, NSCAA First Team All-Far-West Team, College Soccer News First Team All-American selection, All Pac-12 first team, Pac-12 All-Academic honorable mention and Soccer News Net College Boot Player of the Year Finalist. He started and played 19 games at central defense for the Bears and finished the season with 10 goals and one assist. Birnbaum helped lead the Bears to the NCAA tournament quarterfinals.
2012: Was named preseason All-American by College Soccer News, but played just two games for the Bears due to injury. He was redshirted for the season.
2011: Birnbaum was co-captain during his junior season and earned a spot on the All-Pac-12 first team and garnered honorable mention Pac-12 All-Academic status. He started in 16 games for the Bears.
2010: Started in all 20 games for the Bears and finished the season with one goal and five assists. Was a Pac-10 All-Academic Honorable Mention recipient.
2009: Made eight starts as a true freshman, which was the most at the time in school history. He appeared in 17 games.
Birnbaum competed for the U.S. U-18 and U-20 National Team squads in tournaments in Portugal and Mexico in 2008. He was a part of the U.S. squad that competed against Manchester United in the 2008 Milk Cup Final. Birnbaum won a silver medal with the U.S. team in the 2012 Pan Am Maccabi games in Brazil.
Selected in the first round (2nd overall) of 2014 MLS SuperDraft