Armstrong attended Seminole High School in Sanford, Florida. He played both quarterback and safety. As a senior, he led Seminole to the 2008 FHSAA Class 6A state championship over Teddy Bridgewater's Miami Northwestern. During that year he threw for 1,400 yards and 14 touchdowns, rushed for 1,144 yards with 22 touchdowns and caught three passes for 29 yards and one touchdown as a QB. As a safety he had 70 tackles, two interceptions, three forced fumbles and two fumble recoveries. He was considered the 13th best recruit in 2009 by Rivals.com.
College career
Armstrong accepted a football scholarship from the University of Miami. As a freshman in 2009, Armstrong played in 10 games, recording 14 tackles. As a sophomore in 2010, Armstrong took over as a starter and has 66 tackles, three interceptions and a touchdown in 11 games. On July 18, 2012, Armstrong was dismissed from the Hurricanes football team for being dishonest during an internal investigation. On August 14, 2012, it was announced that Armstrong had transferred to Faulkner University and would play for the Faulkner Eagles, an NAIA team, during the 2012 season. However, Armstrong was declared ineligible on September 11, 2012 due to the circumstances of his dismissal from the Miami Hurricanes. NAIA rules prohibit any athlete "who has been permanently banned in a given sport at any four-year institution."
Professional career
St. Louis Rams
Armstrong was signed as an undrafted free agent by the St. Louis Rams after the 2013 NFL Draft on April 27, 2013. He registered 12 special teams tackles. In 2014, he appeared in 4 games. He was released on October 6.
Armstrong was claimed off waivers by the Oakland Raiders on October 7, 2014. He appeared in 11 games. In 2015, he appeared in 10 games. He was cut on November 24, 2015.
On November 25, 2015, Armstrong was claimed off waivers by the San Francisco 49ers. On March 9, 2016, Armstrong signed a one-year contract extension with the 49ers. On September 21, 2016, he was placed on injured reserve with a pectoral injury. On December 19, 2016, Armstrong signed a two-year contract extension with the 49ers through the 2018 season. On November 25, 2017, Armstrong was released by the 49ers.
On November 27, 2017, Armstrong was claimed off waivers by the New York Giants. On October 16, 2018, Armstrong was placed on the injured reserve list after suffering a concussion in Week 6. He appeared in 6 games and registered 20 tackles. He was released on October 23, 2018.
On October 25, 2018, Armstrong was signed by the Cleveland Browns. He appeared in 9 games. The Browns re-signed Armstrong on a one year $1.550 million contract on March 13, 2019. He was released by the Browns on August 31.
On September 18, 2019, Armstrong was signed by the New Orleans Saints after the team placed linebackerAlex Anzalone on the injured reserve list. He appeared in 5 games, playing on special teams. He was released on October 22.
On December 24, 2019, Armstrong was signed by the Dallas Cowboys to provide depth because of injuries for the season finale. He had one special teams tackle against the Washington Redskins. He was not re-signed after the season.
