A new video from New Era Cap Company, Inc., is making the rounds, and for good reason: it’s hilarious. The spot features a pair of popular television and movie stars arguing about a storied sports rivalry. The ad works extremely well for several reasons: it’s funny, it has celebrity endorsements, and it taps into a universal theme the target audience instantly recognizes.

Rivalries are huge in the world of sports. Some rivalries are based on geographical location–fans almost always pledge to hate the nearest competitor. Other rivalries grow over time, after two particular teams or individuals have fought many hard battles against one another. In baseball, the most prominent rivalry of the last couple decades is, without a doubt, the Red Sox versus the Yankees. Any casual baseball fan can tell you that. It can get every bit as heated and passionate as any Republican-vs-Democrat debate.

So when New Era--a leading manufacturer of sports apparel–decided to shoot for a viral video home run, they enlisted a pair of the biggest sports fans around: actors Alec Baldwin (NBC’s 30 Rock) and John Krasinski (NBC’s The Office). Baldwin is a Yankees fan, Krasinski is a Red Sox fan. A few snappy lines of dialog later, and you have this spot:

This ad is brilliant for several reasons:

It hits the target demographic in the sweet spot. Baseball’s 2011 season has just begun, and fans are primed for the sport’s return. Boston and New York even played three rivalry games over the past four days (Boston won two of the three), so this rivalry–which is prominent all season long–is even more front and center right now. (Of course, it would be better if both the Yankees and Red Sox were playing well right now, which neither team is, but New Era can hardly be blamed for the teams’ poor performances to date).

The ad also makes use of two of the most loved and recognizable television stars of the day–each from critically acclaimed NBC sitcoms–and features them prominently on their website:

A little juxtaposition is thrown in, as we get a chance to see rich and famous people do what we average Joe sports fans have done all our lives: trash talk! See… celebrities are just like you and me!

Most of all, the ad works because it’s funny. Even with all the things going for it that I just listed, it would have fallen flat if it hadn’t made people laugh. Thankfully for New Era, it does. Launched late Friday, the clip is already creeping towards half a million views.

Know your target audience. Know them well. It’s not enough to just have customers and be thankful for them. You’ve got to mine their behavior and demographic data to figure out what makes them tick… what motivates them… what they’re passionate about. You can make all the funny videos or the celebrity-endorsement videos you want… until you’ve figured out what motivates your target audience, it’s all just a waste of time. But once you do know your audience… you can put a whole arsenal of proven viral tools to work for your brand.