WAUPACA, Wis. — John Zeamer invested his life savings into a new baseball bat this spring. He paid $250 for a sleek DeMarini Voodoo bat, a model he hopes will help him live up to the nickname Big Country, which he earned for the long balls he hit deep into the outfield.

The investment was not entirely his own decision. Zeamer, 10, and millions of other youth baseball players were forced to dig deep into their (or their parents’) pockets for new bats this season, models stamped with the USA Baseball logo and mandated by new standards issued by the organization.

The changeover has angered parents who have been shocked by the bats’ high costs — $45 to $350 — and frustrated that the demand has seemingly outstripped the supply. Many sporting goods stores and online retailers struggled to stock the approved bats, especially the ones at the lower price points.

Adding to the anger, a popular model made by Easton was decertified by USA Baseball in May, leading the company to offer a $500 e-voucher to anyone who had purchased the bat — but only to spend on other Easton products.

Leah Zeamer, John’s mother, said she was already in deep for this year’s baseball budget.

John wears adult sizes, and everything needed to be replaced: a helmet ($50), two pairs of pants ($70), batting gloves ($20), cleats ($70) and catcher’s gear ($200).

“I wasn’t happy because he just got a new bat last year,” Leah Zeamer said. “I really thought he was set for a while.”

The sale of baseball and softball equipment is big business: It yielded $636 million in revenue in 2017, according to the National Sporting Goods Association, with bats accounting for almost a third of that figure — nearly $208 million. But many of those bats, and millions more bought in earlier years, are no longer legal to use in games.

“USA Baseball, in conjunction with Little League and everybody else, just took everybody’s corner of their garage that had 10 Little League bats in there and basically deleted them from the system with one big standard change in the name of keeping the integrity of the game,” said Brian Duryea, the founder of Bat Digest, the largest independent baseball bat review publication on the internet.

USA Baseball officials said bat manufacturers had no input in creating the standards. The organization also said it had tried to be sensitive to the fact that price is often a barrier to participation.

“This is a transition year, and we knew it would be difficult,” said Paul Seiler, the executive director of USA Baseball. “There’s no plans to do this again in the future, and there are a wide range of prices available out there.”

The change, driven by concerns about competitive balance, was intended to produce a more woodlike standard for the nonwood baseball bats that the majority of young players use. USA Baseball spent several years field-testing bats and parsing data over their “trampoline effects” on a pitched ball to solve what it saw as an imbalance between pitching and hitting caused by high-performance bats.

In other words, hitters swinging engineered aluminum, composite and hybrid bats were crushing pitches and producing too much offense. Why not return to wood bats? Because they tend to break, require frequent replacement and are heavier to swing. For a wood bat to be lighter, it must be thinner, but that creates a smaller contact area at an age when young batters need as much of that area as they can get.

The effort to create new standards for bats began in 2011, when the NCAA switched to the BBCOR bat, which stands for Bat-Ball Coefficient of Restitution, and immediately saw a decrease in home runs. A year later, the standard was adopted by high school baseball leagues.

“The whole idea of bat performance is to regulate that trampoline effect,” said Alan Nathan, a professor emeritus of physics at the University of Illinois and a member of USA Baseball’s standards committee. “Think of bouncing up and down on the ground versus bouncing up and down on a trampoline. You’ll get a much better bounce on the trampoline.”

Youth bats presented a technical challenge because they come in a wider range of sizes to fit a large population of growing children and adolescents. But the change presented a social challenge as well: The bats are purchased by parents and coaches of teams that often are far more conscious of their budgets than high school or college programs.

Tony Rivera, the president of OLS Little League on New York’s Lower East Side, knew that the players on many of his 22 teams were from low-income families or had single parents, so the organization started shopping early, hoping to stockpile newly mandated bats priced at the lower end of the scale.

“We anticipated individual parents would be put in a bind, and we were able to give a couple of bats to each of our teams,” Rivera said. “We got it covered, but not to the extent of what we wanted.”

Although USA Baseball said improved safety did not play any part in the change, the new standard will result in balls coming off the bat slower. The bats, with a barrel of 2 5/8 inches, after all, have been engineered to have less pop.

“Some of the players are so strong and swing so hard that the ball comes off so fast,” said Brian Hoelzel, Waupaca’s police chief and an assistant coach for its 10-and-under travel team. “Last year, we had a player at shortstop get his glove up at the last second, and it hit him in the forehead. You could see the (baseball) stitching in his forehead.”