Although this rivalry is new, many Nationals fans already feel strongly about it. Peter Angelos, the owner of the Orioles, opposed the move of the Montreal Expos to Washington, D.C. on the grounds that it would harm the Orioles financially, contending that the Orioles alone had a legal right to the Baltimore-Washington market. In the four full seasons since the Expos moved to D.C. the Nationals have drawn 9,127,252 fans to the ballpark and the Orioles have drawn 8,892,951 fans to the ballpark.
The Nationals were a larger draw in 2005, the Orioles were a larger draw in 2006 (drawing exactly 100 more fans that year) and in 2007 the Orioles were a larger draw by nearly 200,000 fans. In 2008 the momentum swung back the Nationals way, with the Nationals outdrawing the Orioles by over 370,000 fans, mostly due in part to their then-new ballpark.
Interestingly, the original Washington Senators were well-established in the Baltimore/Washington market for over fifty years before the St. Louis Browns moved to Baltimore to become the present-day Orioles.
Instrumental in that move was the leadership of the Griffith family—then the owners of the Washington Senators.
The dispute with Angelos over the move was resolved when the Orioles were granted the right to broadcast Nationals games on their new television network, the Mid-Atlantic Sports Network. However, the deal was struck only days before the beginning of the 2005 season and many D.C.-area fans did not receive the new network for some time and were unable to watch most games. Furthermore, it has been reported that Angelos and the Orioles hold majority ownership in the network, which has led some Nationals fans to contend that the channel exhibits a bias in covering the Orioles compared to the Nationals (such as displaying the scores of Beltway Series games as "Orioles vs. Washington" as opposed to "Orioles vs. Nationals"). Furthermore, the Orioles changed the name on their away jerseys from "Baltimore" to "Orioles" in 1972 after D.C. lost the last Senators team, in an attempt to convince D.C. fans to adapt them as their team. In 2009, the Orioles changed back to "Baltimore" on their away jerseys.
The tradition of yelling "O!" during the line "Oh say does that Star Spangled Banner yet wave" in the "Star Spangled Banner" is a Baltimore Orioles tradition. Over the years it became a staple of Washington, DC area sporting events. The chant has had controversy in the past and the usage of the "O!" chant at Nationals games has reignited such controversy.