Denver ? The Denver Nuggets do it. So does the University of Colorado. Why not the Colorado Rockies?

The Rockies were following precedent when they began storing baseballs in an environmentally controlled chamber.

The Nuggets use slightly underinflated basketballs because of Denver’s thin air. Balls inflated to normal specifications tend to feel too hard, bounce too high and are difficult to grip.

Likewise, the University of Colorado uses underinflated footballs, basketballs and soccer balls, as well as high-altitude tennis balls, said Mike Smith, CU’s equipment director.

It’s a fact of life in the mile-high city: With less air pressure, adjustments are often required in the equipment to make the game the same at high altitude as it is elsewhere.

“For our games in Denver, our basketballs are slightly underinflated,” said Tommy Sheppard, Nuggets director of media relations. “It’s all based on feel. The visiting team gets a chance to check it, and they can ask for more air or less if they want. It doesn’t behoove us to have a bouncier ball. The ball has to feel the same way it feels in Cleveland or Los Angeles.”

In Boulder, quarterbacks prefer a softer ball so they can get a better grip, Smith said.

If a ball is supposed to be inflated to 13 pounds, “we have to de-air it a little bit,” he said.

There are subtle differences among balls made by various manufacturers, which might explain why the Denver Broncos and the sports teams at Colorado State and the Air Force Academy do not make altitude adjustments, Smith said.

The playability issue prompted the Rockies long criticized for high-scoring marathon games at Coors Field to do something about it.

On March 31, eight days before their home opener, the Rockies began storing baseballs in a humidor to keep them from drying out and shrinking in Colorado’s arid climate and high elevation. The humidor maintains the balls at 40 percent humidity and 90-degree temperature. Major league baseball approved the practice this month.

The Rockies insist they are not altering the ball just preserving it to the manufacturer’s specifications. According to Rawlings, baseballs are supposed to be 5 to 514 ounces in weight and 9 to 914 inches in circumference.

Balls exposed for long periods in Colorado’s climate tend to fall below those specifications. A smaller, lighter ball tends to fly farther. Because they dry out, they also become slicker, making it more difficult for pitchers to grip the balls.

While the Rockies insist it’s too soon to draw conclusions, run production has declined this season at Coors Field. Through 24 games last season, the Rockies and their opponents averaged 15.1 runs per game. Through 24 games this year, the average is 9.3.

Rockies president Keli McGregor said lower scoring wasn’t his primary intention.

“If lower scoring was the desired effect, someone would have figured out something sooner,” he said. “Our original motivation was just to maintain the ball to specifications. We never knew that balls were out of spec before. I thought one of the benefits might be for the pitcher to get a better grip on the ball, a better feel.”

In a test case, McGregor noted that of 12 balls shipped to the Rockies on March 24 and stored as in previous years, 10 have dropped below 5 ounces. Five of the balls have dropped to 9 inches in circumference, but not below that standard yet.

Coors Field now receives shipments of balls about every two weeks. The humidor-stored balls are measured and weighed every week, and the club sends regular reports to major league baseball.

Brian Peko, a physics professor at the University of Denver, said the Rockies are taking the correct approach, but he questioned the 90-degree temperatures under which the balls are stored.

“Humidity makes the balls softer,” he said. “But the higher temperature makes them livelier. Those two effects may be offsetting if the desired result is to make the ball deader.”