Recently, the Washington Nationals, a club that ranked 20th in attendance in 2011, filling on average less than 60 percent of their stadium, announced that there were some fans whose money they'd rather not take.

In hopes of preventing the annual migration of Phillies fans to the Nationals stadium, Washington has implemented a "Take Back the Park" plan that would restrict sales of tickets to 2012 Nats-Phillies games to fans whose credit cards are tied to D.C., Maryland, or Virginia zip codes. The consequences of such a policy are troubling.

From a legal standpoint, the plan is questionable. Although the Nationals are a private organization, Nationals Park is owned and managed by the quasi-public Washington Convention and Sports Authority, which made use of roughly $535 million in public money to erect the facility. Ordinarily, such discrimination against interstate commerce - which the Nationals proudly admit is the case; in fact, that's the point - in favor of in-state commerce would be per se invalid. Absent a ruling that the narrow exception to this principle applied, the Nationals may very well find that they have wandered into the constitutional weeds here.

Beyond the intricacies of the law, however, "Take Back the Park" is simply bad policy.

From its inception, organized baseball has attempted various social-engineering schemes to cherry-pick its desired fan base, often with disastrous and discriminatory results. The National League, itself, was created in 1876 at least partly in an attempt to satisfy club owners' desires to mingle with their social betters, to the detriment of immigrants and the working class.

Upon its formation, NL clubs were required to maintain artificially high ticket prices to discourage attendance of the less-affluent. Also, games were forbidden on Sundays - the only day many working-class fans could attend - and the sale of alcohol was banned. In 1881, the National League expelled Cincinnati from its ranks after it persisted in selling beer to its largely German fan base; this was not the demographic the National League was hoping to attract. To the league's founders, no baseball at all was preferable to baseball played before the "wrong" crowd.

Such tactics endured within the Major Leagues well into the 20th century. After Jackie Robinson officially broke the game's color barrier in 1947, every team maintained unofficial racial quotas for years, in some cases decades, due to owners' fears that "too many" black players would upset their predominantly white fan base. This not only limited the racial diversity of the game's fans, it also kept hundreds of qualified black players off Major League teams despite Robinson's achievement.

Of course, "Take Back the Park" is not rooted in racial or socioeconomic ideology; the Nationals simply want to prevent hordes of Phillies fans from transforming Nationals Park into Citizens Bank Park South again in 2012. But history shows that trying to decide who is an appropriate fan and who is not is fraught with peril.

Tying one's ability to purchase a ticket with his or her zip code can lead to many possible outcomes, most of them bad. If research showed that fans from more affluent zip codes spent more money once inside the park on concessions and souvenirs, would clubs then seek to prevent, or at least delay, fans from less-affluent ones from purchasing tickets? The racial implications of such a tactic, given that de facto societal segregation, often by zip code, is an unfortunate reality in many areas throughout the nation, also cannot be blithely set aside.

Major League Baseball should put a stop to "Take Back the Park," along with any other attempts by clubs to rig the makeup of their audiences. Customers are customers, regardless of whether they root for the home club, the opposition, or nobody. Besides, if the Nationals really want to fill their park with local fans, they should try a tactic that has proved foolproof since the 19th century: Put a decent club on the field.

Mitchell Nathanson is a professor at Villanova Law School whose book, A People's History of Baseball, will be published in March. E-mail him at nathanson@law.villanova.edu.