Bill Hamid made history on September 2, 2009, when he became the first D.C. United Academy player to sign with the first team. Prior to signing with D.C. United, he was linked with a move to Celtic, until work permit issues derailed the move.
He made his professional debut on May 5, 2010 in a game against the Kansas City Wizards. With this win, Hamid became the youngest goalkeeper in MLS history, at 19 years 161 days, to win a regular season game, besting Tim Howard's record by four days. Hamid started 28 of United's 34 games during the 2011 season. He retained his starting spot during the 2012 season, making appearances in 27 matches, while also receiving red cards on two occasions for fouling attacking players - on July 15 in a regular season game against Houston Dynamo and on November 9 in a 2012 MLS Cup Playoffs match vs. New York Red Bulls.
In 2012, Hamid earned a record 88 saves in arguably his best season in the MLS to date. Despite Hamid being sent off with a red card during the 2012 playoffs in a match against the New York Red Bulls, D.C. United was able to come away with a win and advance to the next round. Hamid, emotional after seeing the win, was video taped shirtless screaming "You can't hold us back" while pounding his chest. The phrase became a rallying cry for D.C. United fans who organized a display featuring the quote. Although D.C. United failed to defeat their next challenger, the Houston Dynamo, the phrase stuck with the fans. For the 2013 season, the D.C. United fan group Screaming Eagles designed a scarf with the quote and presented Hamid with a free one.