In 2005–06, Green split the season with the Capitals and their American Hockey League (AHL) affiliate, the Hershey Bears.

He scored his first career NHL goal against Ed Belfour of the Toronto Maple Leafs on February 3, 2006,[1] and finished with three points in 22 games for the Capitals.

Green earned the nickname "Game Over," made popular by play-by-play announcer Joe Beninati after his game-winning goals in the last minutes of the third period or overtime became a regular occurrence.

Green did not start his goal-scoring run until after Bruce Boudreau replaced Glen Hanlon as head coach on Thanksgiving Day, 2007.

In Game 3, on April 15, Green recorded a Gordie Howe hat trick (a goal, an assist and a fight) in a 6–3 loss to the Philadelphia Flyers.

During the 2008 playoffs, Green's signature "faux hawk" hairstyle received increased publicity as his profile in the NHL was raised.

An Elliot in the Morning promotion, "Rawk the Hawk," had Green into the studio for the haircut, which willing fans could also have done for playoff tickets.

The D.C. morning talk radio show brought this promotion back for the 2009 season, offering tickets for the first game of each new series.

[citation needed] At the end of the season, on May 21, 2008, Green was named to the Sporting News' NHL All-Star team along with teammate Alexander Ovechkin.

[12] In April 2009, Green was nominated for the James Norris Memorial Trophy for the NHL's top defenceman, along with Zdeno Chára and Nicklas Lidström.

Still a far-cry from his output in previous years, Green played an integral role in the capitals playoff run with the services of Dmitry Orlov being unavailable for the entire season.

[21] On February 24, 2020, Green was traded to the Edmonton Oilers in exchange for Kyle Brodziak and a conditional fourth-round pick in 2020.

[25] Following his break-out season with the Capitals, Green debuted for Team Canada at the 2008 IIHF World Championship as the host country.

He is raising money for Children's National Medical Center as part of America's Giving Challenge, sponsored by Parade magazine.