Many possible reasons for decline in big flies

And now for a change of pace, here's a story on players making news by not hitting the ball over the fence.

While Barry Bonds steps up his pursuit of Sadaharu Oh, Frank Thomas and Alex Rodriguez revel in their 500th home runs and Jim Thome and Manny Ramirez prepare to join the club, this might go down as the season in which the warning-track fly ball became fashionable.

Check the statistics, and you'll find a slew of brand-name sluggers failing to produce to their usual standards. Although the list doesn't quite run from A to Z, most of the alphabet is covered on our journey from Jason Bay to Travis Hafner to Derrek Lee to Vernon Wells.

As the wild-card races heat up and baseball barrels toward another attendance record, home run symbols from the Citizens Bank Park liberty bell to the Shea Stadium apple are too often dormant these days. At least Bernie Brewer's posterior is getting a workout on the Miller Park outfield slide thanks to Prince Fielder and Ryan Braun.

Some noteworthy examples in a relatively fireworks-free season:

• Based on the numbers through this past weekend's games, the 30 big league clubs are on track to hit 578 fewer home runs than in 2006.

• Last season, 11 big league hitters surpassed 40 homers. This year, only four players (Rodriguez, Fielder, Ryan Howard and Adam Dunn) are on pace to hit 40.

• Baseball's aggregate slugging percentage has dipped from .432 to .418.

• Boston's Ramirez and David Ortiz have combined for a home run every 21.2 at-bats after going deep once every 11.3 at-bats in 2006. They've hit 38 homers after connecting 89 times in 2006.

Vladimir Guerrero's Home Run Derby title was sandwiched inside a 30-game, 125 at-bat long-ball drought. During his five-week fallow stretch, Guerrero was out-homered by Josh Paul, Michael Bourn, Jeff Bailey, Jason Tyner and Micah Owings -- who had one each.

It's only fitting that Giants broadcaster Duane Kuiper, who during his major league career hit one homer in 3,379 at-bats, was the guy who waved Bonds' 756th out of the yard.

The people at Major League Baseball's central offices in New York have taken notice, but they're unable to pinpoint the cause for the decline. They can only make assumptions on the data, and the explanations are primarily "anecdotal," said Jimmie Solomon, MLB's executive vice president of baseball operations.

"You can't put a finger on exactly what creates a power surge or a power decline," Solomon said. "People have various opinions about it, I'm sure."

Here are some possible explanations sure to be part of any debate:

Steroid withdrawal

Baseball's steroid craze led to outrage in Congress and an investigation by former Sen. George Mitchell. It's the reason Greg Anderson is in jail, Bonds is dogged by questions about the legitimacy of his home run record and Mark McGwire won't be stopping by Cooperstown anytime soon.

If steroid use fueled a home run binge in the late 1990s and early 2000s, isn't it logical to assume that a ban on performance-enhancing drugs would result in a decline? Perhaps, but that argument seems overly simplistic to some.

"People from the outside looking in must think, 'Drug testing is starting to work,'" Atlanta pitcher Tim Hudson said. "But you never know what guys are dealing with. You don't know if they're dealing with injuries. There is such a thing as guys having down years. Guys get older. It's a combination of things."

Houston outfielder Lance Berkman concurs.

"You're going to have years where a guy will lead the league with 110 RBIs, and the next year somebody will drive in 150," Berkman said. "Even before the steroid scandal, that was the nature of the sport."

The steroid argument appears flawed because the new testing program began in 2004, and two years later, power production significantly increased. So why would home run totals suddenly fall now?

Pick a point of view, and chances are someone subscribes to it. One American League scout suspects that players who have used performance-enhancing drugs for years and escaped detection might finally be breaking down from all that extra stress on the joints. It's the old "what goes around, comes around" theory.

A National League scout suggests the power dip is less attributable to steroids than amphetamines, which were first outlawed in 2006.

"I think some guys are tired," the scout said. "It was real easy for a player to say, 'I'm not going to take steroids, but a little greenie now and then doesn't hurt.' The use of greenies was more prevalent than people think."

Of course, pitchers took amphetamines, too. But even workhorse relievers rarely pitch more than three or four times a week, so at least they have some time to recuperate.

Mother Nature

Dave Lawson, a statistical consultant for Milwaukee and Texas, points out that offense peaked in 2000 and has generally been slipping ever since. Last year's power blip -- not this season's decline -- was the aberration.

Lawson contends that offensive cycles generally span decades (the 1930s, '50s and '90s were particularly kind to hitters) and are related to climate changes. In a nutshell, hot, thinner air helps a baseball travel farther. Cool temperatures and denser air are a deterrent to offense.

"It has nothing to do with steroids, in my opinion, and a lot more to do with the weather," Lawson said.

Denser air can benefit pitchers in another way: Because there's greater resistance, the ball moves more and is tougher for batters to track and hit.

In a Hardball Times essay in May, Chris Constancio wrote that the average temperature in major league cities in April was 58.2 degrees -- more than four degrees cooler than the previous two seasons. You don't have to look hard to find hitters who'll bemoan the adverse conditions in the opening month.

"It's tough to even swing when it's 30 degrees," Atlanta's Mark Teixeira said. "We had some real cold days, and that didn't help."

Father Time

Braves outfielder Jeff Francoeur hit 29 homers last season with a disappointing .293 on-base percentage. Before this season, he decided to change his approach and concentrate on being more selective and hitting the ball the opposite way.

As a result, he's become a more polished hitter. Francoeur ranks 10th in the National League in RBIs and has more doubles and a significantly higher on-base percentage this season.

Francoeur is 23 years old, so a one-year dip in home run production is no cause for alarm. But lots of power hitters have reached a point where they're fighting age every step of the way.

Ramirez, Carlos Delgado and Chipper Jones are all 35. Thome is 36, Ken Griffey Jr. 37, Gary Sheffield 38 and Thomas and Jeff Kent are 39. Several players who could be penciled in for 30-plus homers a season aren't such bankable commodities anymore.

For all the talk about advanced training and longer careers today, bat speed doesn't necessarily last forever. Did somebody say "Greg Vaughn"?

"When you get older, your body breaks down," Francoeur said. "I've seen it with Chipper this year. As he gets older, he really has to take care of himself. When you play that long every year, it gets tiring, I'm sure."

The old horsehide

Big offensive seasons invariably bring out the juiced-ball conspiracy theorists. So what's going on when long fly balls are dying at the track?

In most respects, the baseball this season is no different from previous seasons. The parts are manufactured in the U.S., then assembled at a factory in Costa Rica. Solomon said MLB plans to send a contingent to Costa Rica shortly on a routine inspection.

But this season, for the first time, MLB required all 30 clubs to keep baseballs in climate and temperature-controlled rooms. Colorado is still the only team with a humidor, but Solomon said other clubs have humidity controls in their baseball storage areas.

Furthermore, MLB also decreed that any balls purchased by teams in 2006 can be used only for batting practice. Leftover balls aren't kosher in actual games.

Could the new guidelines for uniform baseball storage be a factor in the offensive decline? Solomon won't rule out that link.

"When you were a kid and your mom made you keep your equipment in a storage room where they had no climate control, remember what your baseball felt like later?" Solomon said. "If it had been raining a lot, it felt heavier. If it was really dry, it felt lighter. Everything is impacted by the elements."

For what it's worth, Hudson and Mets closer Billy Wagner said the baseballs don't feel any different this season. Cleveland outfielder Trot Nixon recently told a Washington Times reporter that inferior bat quality might be a factor, but Wagner shrugs off that theory.

"Nope," Wagner said. "They're still triple-dipped, just like always."

The injury bug

You could stockpile two Home Run Derby fields with all the sluggers who've spent time on the disabled list this season. The list includes Thome, Howard, Teixeira, Jones, Troy Glaus, Hideki Matsui, Chase Utley, Alfonso Soriano, Aramis Ramirez, Miguel Tejada, Carlos Beltran and Eric Chavez.

Other players have managed to play through injuries while avoiding the disabled list. Sheffield and Ortiz both received cortisone shots in their aching shoulders last week, and Travis Hafner has been bothered by tightness in his left knee.

You know it's a strange year when Griffey, with eight disabled list visits since 2001, stands out as a monument to good health.

Better pitching

It's hard to say pitching is better when the Phillies felt fortunate to acquire Kyle Lohse at the July 31 non-waiver deadline. But there's a school of thought that pitching has improved through an influx of young arms and a newfound focus on craftsmanship over radar gun readings.

"I think pitchers are doing a great job of being smart with power hitters," Teixeira said. "I've had a lot of 3-2 counts and instead of getting that fastball down the middle, I might get a backdoor slider or a changeup down and away. The pitchers are doing a good job of mixing it up."

When Trevor Hoffman saves his 500th game, Tom Glavine picks up his 300th win and Jamie Moyer keeps plugging away in 80-mph increments, the soft-tossing geezers are setting a fine example for today's youth. Even Wagner is changing speeds more often in an effort to be more economical.

"I think more guys are saying, 'I'm giving up five or six runs every outing throwing to that [radar] gun. Now I'm going to back off a little and locate my stuff,'" said Dan Jennings, vice president of player personnel for the Florida Marlins.

Conventional wisdom is that offense thrives during expansion. After the arrival of two new teams in 1993 and two more in 1998, have we had enough of a breather for the pitchers to finally catch up to the hitters?

Stuff happens

Pittsburgh's Adam LaRoche hit .133 with three home runs in April, then conceded he might have been trying too hard to impress his new teammates.

Wells has 14 homers in 449 at-bats. Is he putting too much pressure on himself to justify his $126 million contract?

And what about Delgado? Barring a late rush, he'll fall short of 30 homers for the first time since 1996. Is he suffering the effects of offseason wrist and elbow surgery? If so, he won't admit it.

"I'm healthy," Delgado said. "I just think my timing has been off. I was pretty jumpy for a good 2½ months. It's tough to drive the ball when you're jumpy like that."

Berkman knows the feeling. In 2006, he bonded with his swing early in spring training and hit 45 homers for Houston. It seemed as if the umpires called every borderline pitch a ball, and every time Berkman swung, the pitch was sitting on a tee.

This season, in contrast, has been a grind from the outset. Berkman had three extra-base hits in April, got caught up in a "negative cycle," and has been fighting his swing every day.

"I feel like things have been in a tangled mess for the entire season, and I can't figure out how to untangle them," he said.

Berkman, incidentally, went deep for the 21st time this season in a 6-4 win over Milwaukee on Sunday. If he's a mess, just imagine how some of these other guys must feel.

Jerry Crasnick covers baseball for ESPN.com. His book "License To Deal" was published by Rodale. Click here to order a copy. Jerry can be reached via e-mail.