In the end, professional sports live off their fan base and its loyalty. When the fans stop showing up, stop following their team’s season and stop buying the hats and T-shirts, the team is in trouble.

Major League Baseball has a problem in that regard.

There will always be franchises in every sport that struggle to make it. All franchises will have their up and down years financially and at the gate. What pro sports can’t endure is a general malaise that settles over the fans where they can take or leave the sport or their team.

That has happened in Arizona with the Diamondbacks, in Florida with both of its teams (Devil Rays and Marlins), in Chicago with the White Sox, in San Diego, Montreal, Minnesota, Toronto, Oakland, Detroit and Kansas City. It may be happening in Cincinnati and Houston.

The D’Backs are a prime example. They came on line just four years ago with all the hoopla of new age baseball in the desert. Buck Showalter, the manager in waiting, worked the public for two years before the team ever played catch. Banners and signs, memorabilia and publicity surrounded the team years before it every went to its first spring training.

Arizona was touted by MLB as the way to kick off a new franchise. The team was a hot item, selling the hats and shirts at an amazing rate.

Then came reality.

Attendance has dropped each of the last three years. The season ticket base was off 25 percent after the first year. The Arizona public got bamboozled into putting money into yet another stadium for another millionaire. The cost overruns came, the team’s payroll rocketed, and the club has had to borrow $60 million to stay afloat.

San Diego has a hole in the ground where more public money was supposed to be dumped for a new ballpark that is now caught up in local politics. The team flim-flammed the fans. After losing the 1998 World Series, they herded the players back on the field to beg for votes for the tax money to build the new park, and then commenced to break up the team.

Folks in Toronto came to see Sky Dome and forgot there was a team that played there.

Montrealers have suffered with the worst park in baseball for fans: a dark, dank dungeon but for Olympic runners, but not bats and balls. They stay away in droves.

In all of these situations, fans have come to recognize one stark truth: they come last.

The Red Sox, Yankees, Cubs and a handful of others still have loyalty passed on from one generation to the next. In the Red Sox’s case, it’s geographical. For the Yankees, it is the city and the winning.

Negotiations for a new labor agreement in baseball are quietly under way. The old one expires this year.

For both the players and the owners, there had best be a recognition that they must reach out to fans again and give them a reason to care.

Franchises need players who will be there for a while to connect the team to the fans. Both sides have to find a way to be financially responsible. The Frank Thomas, Gary Sheffield and Barry Bonds salary whining society isn’t helping anyone.

When the caring stops, the games end.

Major League Baseball is heading in that direction.

Old Town native Gary Thorne is an ESPN and CBS sportscaster.