For golfers, the difference between a Callaway and a TaylorMade club, “is like asking ‘What’s a better car—BMW or Mercedes?” says David Braham, president of the World of Golf store in New York. “The two companies compete, and they’re both very good, but when a customer picks one club over the other, it just comes down to what kind of person you are.”

For the executives who run Callaway and TaylorMade, the difference is vast—and personal. “He’s not a golfer,” snipes TaylorMade C.E.O. and scratch golfer Mark King, of Callaway C.E.O. George Fellows. “While I have every respect for him, he doesn’t have any real interest in the game.”

The rivalry between the two top equipmentmakers teed off more than a decade ago, but the competition has grown more intense as growth in the industry as a whole has slowed. Adding to the tension for these two companies is their proximity to one another: Both Callaway and TaylorMade, which is owned by German sporting-goods company Adidas Group, are headquartered in Carlsbad, California. Executives from both firms often dine at the same place—the popular local brewery and restaurant Karl Strauss—but at distant tables.

The numbers show a close competition between the two companies. Callaway has consistently led the market in irons with about 25 percent of the U.S. market versus 16 percent for TaylorMade, while TaylorMade dominates in metal woods (a 26 percent market share to Callaway’s 19 percent). Both companies have actually managed to increase their market share slightly in recent years, meaning that even as they’ve battled each other, they’ve also taken share from their competitors such as Cobra, Ping, Adams Golf, and Cleveland Golf.

In terms of overall earnings, the two companies are relatively close as well. Callaway’s first-quarter sales this year increased 9.5 percent to $366.4 million, while TaylorMade reported a 6 percent increase in sales to 191 million euros for the same period, or about $296 million.

But recently, a bigger challenge has emerged: The U.S. golf industry as a whole has flattened. The number of golfers in the U.S. has stayed virtually the same in the last few years, hovering between 28 and 29 million, according to the National Golf Foundation. Tiger Woods’ ascendance in the late ’90s boosted golf’s popularity significantly, but his impact has proved to be a temporary. In the last two years, for instance, 232 new courses were developed while 268 closed, which means that for the first time in U.S. golfing history, there was a net loss in courses, according to the National Golf Foundation.

Industry analyst William Chappell of Sun Trust Robinson Humphrey estimates that the golf-equipment industry has grown at just 2 to 4 percent annually since 2000. “It’s not considered a growth industry,” Chappell says.

No wonder the battle is so personal.

“We’re about the game of golf,” insists King, who played on his college team. “[Callaway] is about the business of golf. We position ourselves around what’s authentic to golfers—not what’s a clever way of marketing your product.”