Davy made his debut against Metapan in El Salvador in a 3-1 victory for Colorado Rapids, coming on as a substitute for Eddie Ababio.
[4] On August 1, 2013, Armstrong was loaned to third-tier Phoenix FC for the remainder of their USL Pro season.
[5] On February 4, 2015 it was announced that Armstrong was going start playing for USL Pro team Colorado Springs Switchbacks FC, he was the 10th player announced for the Colorado Springs Switchbacks FC[6] Armstrong played 23 games for the Colorado Springs Switchbacks FC in his first season with the club, and recorded 2 assist.
[7] On January 20, 2016 it was announced that Armstrong re-signed to the Colorado Springs Switchbacks FC for the 2016 USL Pro season.
He qualifies through his Cambodian father who immigrated to the United States during the Vietnam War.