After graduating from Peekskill High School, Armstrong started off slowly as a college athlete, averaging under 4 points in each of first 3 seasons at UConn with the Huskies. However, he greatly improved in his senior year, averaging 9.7 points, 6.6 rebounds, and 3.1 blocks, and shooting 61% from the field. He followed after his teammate Josh Boone, and won the Big East Defensive Player of the Year award in the 2005–06 season.
Professional career
NBA (2006–2011)
He was declared eligible for the 2006 NBA draft, and was selected by the New Orleans Hornets with the 12th overall pick. Known for his shot-blocking and athleticism, he was anticipated by analysts to be an instant contributor to the Hornets front line, but the team then traded for the Chicago Bulls center Tyson Chandler. Chandler was named the starting center and Armstrong played a reserve role throughout his time with the Hornets. On January 11, 2010, Armstrong was traded to the Sacramento Kings for a conditional 2016 second-round draft pick. On February 18, 2010, Armstrong was traded to the Houston Rockets, along with Kevin Martin, for Carl Landry and Joey Dorsey. He was waived by the Rockets on April 10, 2010. Armstrong signed with the Washington Wizards on July 13, 2010. On February 23, 2011, Armstrong was traded to the Atlanta Hawks, along with Kirk Hinrich, in exchange for Mike Bibby, Jordan Crawford, Maurice Evans and a first-round pick in the 2011 NBA draft.
On January 2013, Armstrong was acquired by the Santa Cruz Warriors of the NBA D-League. He played very well for the Warriors, earning 2nd Team All D-League Defensive Team honors. On September 27, 2013, he signed with the Indiana Pacers. However, he was waived on October 26. In November 2013, he was re-acquired by the Santa Cruz Warriors. On December 11, 2013, after playing in six games with Santa Cruz, Armstrong signed with the Golden State Warriors. On December 29, 2013, he was waived by Golden State. On January 3, 2014, he was re-acquired by Santa Cruz. On February 3, 2014, Armstrong was named to the Futures All-Star roster for the 2014 NBA D-League All-Star Game. On February 22, 2014, he signed a 10-day contract with the Golden State Warriors. On March 4, 2014, he returned to Santa Cruz after his 10-day contract expired. On March 30, 2014, he signed another 10-day contract with the Golden State Warriors. On April 9, 2014, he signed with Golden State for the rest of the 2013–14 season. He started the final game of the regular season and recorded a double-double. On July 30, 2014, he was waived by Golden State. While playing for Golden State, Armstrong became the first player in NBA history to wear jersey number 57.
Turkey (2014–2016)
On August 6, 2014, he signed a one-year deal with Turkish team Beşiktaş of the Turkish Basketball Super League. On May 5, 2015, Armstrong recorded a career-high 30 points, shooting 10-of-14 from the field, along with nine rebounds, three assists and three steals in a 74–94 blowout loss to Fenerbahçe. On July 30, 2015, he signed with Tüyap Büyükçekmece also of Turkey. However, on November 10, 2015, he parted ways with Büyükçekmece and joined Denizli Basket of the Turkish Basketball First League for the rest of the season.
Japan (2016–2018)
On August 5, 2016, he signed with the Japanese team Chiba Jets of the B.League. In 60 games played for the Jets, Armstrong averaged 10.2 points, 7.7 rebounds, 1.6 assists and 1.4 blocks per game. On July 28, 2017, he signed with the Ryukyu Golden Kings for the 2017–18 season.
Israel (2018–2019)
On August 16, 2018, he signed a one-year deal with the Israeli team Bnei Herzliya, joining his former teammate Jeff Adrien. However, on January 10, 2019, Armstrong parted ways with Herzliya after appearing in 13 games.
