My memory is not so good but it seems to me that professional golfers didn’t used to look so much like race cars.

Perhaps they have been consulting with auction theorists.  Selling ad space on your shirt is like a multi-unit auction but with an interesting twist.  Like any auction you want to insist on a reserve price to keep revenues high.  The reserve acts as a threat not to sell unless bids are high enough and this induces more agressive bidding.  Normally this leads to under-supply, just as a textbook monopolist restricts output to keep prices high.

But here’s the twist.  After you have sold the ad on your hat, your auction for an ad on your lapel is a threat against the advertiser on your hat.  If you sell an ad on your lapel it’s going to take some focus off the hat.

That means it is in both yours and the hat-advertiser’s interest to have him bid for the lapel ad.  Yours because more competition is better, and his because he wants to keep the competitors off your lapel.  Now think about how your reserve price for the lapel-auction works.  Just as before, for the new bidders it is an inducement to bid higher.  But for the hat-guy it’s an inducement to lower his bid for your lapel.  If you set a high reserve then he can safely lose the auction for your lapel and expect that nobody else will win, which for him is just as good as winning.

This leads you to set a lower reserve on your lapel than you otherwise would.  In effect this is a threat to the hat-hawker that if he doesn’t bid high enough to keep your lapel clean, you are going to put someone else’s logo there.  That is, you are over-supplying ads (relative to the situation in which the ads had no spillovers.)

When these principles are put to use, two kinds of outcomes can occur.  If there is a high enough bidder you will sell exclusive advertising to that bidder.  If not, you will sell lots of little ads to little bidders.

While we are on the subject, here are recent prices for apparel real-estate.