The scene: Boston's Fenway Park

The seats: Twenty-five rows behind home plate.

The players: The Red Sox vs. the Yankees in their first series since the All-Star Game.

It's a Friday night and my co-worker, Lee, and her brother have traveled from separate cities to meet in Boston to renew their shared childhood passion of baseball. This is the first game they've watched together in nearly 25 years, but they soon settle into their roles -- she keeps score; he keeps even closer tabs on the action -- as if time has stood still.

The pitch: David Wells is on the mound facing the heart of the Yankees' order. The windup. The pitch. Lee sees what she thinks is a passed ball but the official scorer rules it a wild pitch. She turns around to get her brother's take . but her brother's not in his seat.

The Sox's 17-1 win turns into the kind of game you tell your grandkids about. Trot Nixon hits an inside-the-park homer; David Ortiz hits a grand slam off Buddy Groom.

But that's not the game Lee's brother saw that night at Fenway.

Fenway Park, Take Two
The scene: The belly of Fenway.

The players: Concession-stand workers, memorabilia hawkers, ticket takers, ushers, janitors, and bored baseball game dates.

The din of the crowd is white background noise to the action beneath the bleachers. The under-stadium pathway circling Fenway is dotted with colorful kiosks staffed with brightly smiling teams of representatives tempting passersby with Red Sox wares.

But you can't buy this memorabilia with cash. These vendors require more valuable currency -- your signature.

The pitch: Want a Red Sox blanket? No problem. Just fill out this application for an MBNA (NYSE:KRB) credit card and please sign on the dotted line. After all, real fans want every checkout clerk to know where their allegiance lies.

Schwag sells
The scene is the same in baseball stadiums across the country. Simply substitute the Sox Visa for the Seattle Mariners or the Dodgers MasterCard in place of the San Diego Padres plastic. Enjoy your logo-laden fishing hat or T-shirt or Frisbee or tote and in three to six weeks (pending approval), your new credit card will arrive in the mail.

At one point Lee's brother had nearly a full deck in his card collection: 27 credit cards -- granted, not all from ballparks, but just three ballparks shy of a major league sweep -- and enough team logo schwag for several Christmases.

If baseball's not your bag, don't worry. There are thousands of credit cards emblazoned with everything from college campus scenes to kittens in a basket. From the Sox to Spiderman; the Dodgers to a Hillary Duff pre-paid credit card, there's a credit card dressed up for nearly every interest. The industry calls them "affinity programs" -- co-branded credit cards designed and marketed to specific groups.

Affinity cards are just regular credit cards color-coordinated to the cardholder's interests. Some have perks customized to appeal to that group's demographic, such as donations to a particular cause or discounts on team tickets or products. I have an MBNA Visa emblazoned with The Motley Fool logo in my wallet that gives me cash back for every purchase. (I've found cash to be a pretty generic but appealing perk.)

MBNA is one of the biggest affinity card issuers, but all the major players use alma maters, hobbies, celebrities, even dog breeds to up the appeal of their credit cards.

If you think that the schwag they manufacture to attract applicants costs the credit card companies a bundle, you're right. But a Red Sox blanket is a lot cheaper than the alternative.

Lenders spend anywhere from $50 to $150 to acquire each new customer. That number takes into account fliers, co-branded partnerships, commercials, and those ubiquitous mass mailings (expected to reach 6 billion a year) clogging your recycling bin. All that to get less than 1% of recipients to open the envelope and sign on the dotted line.

The Red Sox lap blanket Lee's brother got that night? It was far from free.

Who's keeping score
A credit card application is like a tattoo; a short-term decision with very long-term results.

When you apply for a line of credit, you trigger a "hard inquiry" when the lender takes a gander at how you've handled borrowed money in the past. No matter if you're approved or denied, that notation signals that you were shopping around for a loan. (When you check your own credit, it appears as a "soft inquiry" and does not affect your credit score.) Too many hard inquiries can begin to bring down your credit score faster than a bad pitch to the shin.

Inquiries linger in your file for about two years. It's when you get approved for a line of credit that you learn the meaning of "long-term consequences." Every line of credit in your name is reported to one (or all three) of the credit reporting agencies (Equifax (NYSE:EFX), Experian, and TransUnion). That Red Sox Visa card -- even if canceled right away -- will be on Lee's brother's redit report for at least seven years.

Oh, but it's not just potential creditors and older sister raising eyebrows about your penchant for Major League Baseball team credit cards. Your existing lenders regularly check in on you . and if they see you acquiring a lot of additional lines of credit (they don't know that you did it just for the free team baseball), you'll be flagged as a potential credit risk. They'll raise your interest rate -- yes, even that special low APR offer -- to cover their own keisters.

Lenders aren't the only ones keeping tabs on your credit scorecard. Landlords, employers, utility companies, and anyone else with a permissible business purpose can use your credit report as a means of sizing you up. (At least you can see who's been checking on you. Your credit report lists companies that have made recent inquiries.) According to the Federal Trade Commission, over the course of a typical workday, about 2 million credit reports are requested by companies going about their business.

If you don't keep close tabs, that flier you filled out at the ballpark will turn into a butterfly-flapping-its-wings scenario in no time.

Be a player-manager
When it comes to keeping score, lenders have an exacting way of seeing how you measure up. But you can play along at home by ordering copies of your credit report from the three major reporting bureaus. (Residents of most states can do so for free under the Fair and Accurate Credit Transactions Act.)

By memorizing a few pages from the playbook lenders use, you can whip your credit into shape before next baseball season. The good news is that the more distance between you and your heat-of-the-moment ballpark blunders, the more forgiving bankers get. (Fool community members recently hashed out how long it takes to repair dinged credit.)

The next time you go to the ballpark, ask yourself what you'd rather take home: a free team logo mug or memories of a grand slam.

More inside credit .

If you're planning any banking maneuvers within the next three to nine months, it is worth the price of admission to order your credit report now. Motley Fool Credit Center sponsor TrueCredit offers readers a single report with data from the three major credit reporting agencies, as well as one free credit score, for $29.95.

Dayana Yochim owns none of the companies mentioned in this article and is a fan of Major League Shopping.