On baseball's biggest stage, one of its best pitchers broke out one of its most controversial training methods. Aroldis Chapman, he of the 105-mph fastball, was seen throwing off the mound in the Cubs' bullpen prior to each of his World Series appearances with -- insert audible gasp here -- a 10-ounce weighted ball.
It's not a new thing for Chapman. Really, it's not a new thing for baseball.
Dr. Mike Marshall, who pitched in 106 games for the Dodgers in 1974, began throwing weighted balls (a standard ball is 5 ounces) into a mattress hung on the fence in the early 1970s. Indians pitching coach Mickey Callaway used a 5-pound ball beginning when he was 14 years old, and he remembers teammate Jeff Sparks using a 15-pound ball while with Tampa Bay in 1999 (Working with that ball to strengthen the arm actually isn't as crazy as it sounds. For reference, a men's shotput weighs 16 pounds).
Relievers Mariano Rivera and Armando Benitez warmed up with weighted balls before each of their appearances, and former Yankees pitching coach Mel Stottlemyre says nearly every Cuban pitcher he saw while with the Yanks from 1996-2005 used weighted balls as part of their training program. Currently, weighted balls are used -- regularly and openly -- by Chapman, Seattle's Felix Hernandez, Cleveland's Corey Kluber and Trevor Bauer and Baltimore's Zach Britton, among others.
A new study by Dr. Glenn Fleisig at the American Sports Medicine Institute in Birmingham, Ala., which is the research wing of Dr. James Andrews' practice, advances the cause of those who believe using weighted balls is, indeed, the wave of the future.
Video: Lindsay Berra discusses players using weighted balls
"The force on the elbow actually goes down as the weight of the ball increases," Fleisig said. "With a heavier ball, the arm moves more slowly. Newton told us that 'force equals mass times acceleration.' A heavier ball has more mass, but the arm is moving a lot slower, so throwing a heavier ball actually correlates with decreased arm forces and torque."
Fleisig concluded that throwing slightly underweight and overweight baseballs is not only a reasonable exercise for baseball pitchers, but also that the variation from the normal routine of throwing a 5-ounce ball serves to increase awareness in the nerves and muscles and can make a pitcher more effective when he returns to the standard baseball.
"It makes sense to vary things a little," Fleisig said. "Mechanics with the lighter and heavier balls are similar enough not to learn anything bad, and tweaking is good for training. It's a wake-up call for the body to pay attention."
Perhaps the study will change the mindset of wary big league clubs. Kyle Boddy of Driveline Sports in Seattle uses the balls extensively as a training method. He works with Bauer and more than 80 other professional pitchers who all have a very different experience when they arrive at Spring Training with their weighted baseballs.
"When players show up at camp with their weighted balls, I'd say one-third of teams are openly excited and say, 'Great, here's a place to throw them,"' Boddy said. "Another third would be wary, tell them, 'OK, but please don't get hurt.' And another third would just take them away. Some clubs are still very, very restrictive."
The Phillies, Marlins, Royals and Pirates are among clubs that have been wary of using this method, with the fear that training with weighted balls -- both underloaded and overloaded -- creates too much stress on the elbow and can cause injury.
"The Phillies are not promoters of the weighted balls," Phils Minor League pitching coordinator Rafael Chaves said.
Eric Cressey of Cressey Sports Performance in Jupiter, Fla., has been using weighted balls to train pitchers since 2007, and he has been training '14 American League Cy Young Award winner Kluber with them since '11. Cressey also gets varied reactions from big league clubs.
"Some teams are very alarmist and fly their staffs down here once a month to check on their pitcher and measure their range of motion," Cressey said. "Others are very open-minded and are totally fine with it."
The Orioles are in the latter camp.
Britton started with weighted baseballs as a teenager, when Flint Wallace of Ron Wolforth's Texas Baseball Ranch was his coach at Weatherford High School. Britton -- and subsequently, many of the Orioles' other relievers -- can be seen warming up in the bullpen before every outing with a green 32-ounce baseball. During the offseason, for most of December and January, Britton uses a full weighted baseball program in which he throws heavier baseballs -- 6, 8, 10, 12 and 32 ounces -- against a padded fence or wall, from a distance of no more than 30 feet. Britton also throws underloaded 4-ounce balls.
"Shoulder strength and arm speed is what I'm looking for," Britton said. "I think the drills where you have to control a little bit more weight have helped with my shoulder stability, and using the lighter ball makes me feel faster and more flexible. For me, it's definitely a piece of the puzzle."
It's a piece at least a few teams are incorporating. The Dodgers conducted their own experiment with Driveline, and they sent a group of Minor League pitchers who had struggled with injuries and loss of velocity to train with Boddy and his weighted baseballs for 10 weeks last spring. Nearly all of them -- including David Reid-Foley, Andrew Istler and Corey Copping -- returned to pitching off a mound and saw an increase in velocity.
"We're bullish on any programs that encourage us to train with great intent and intensity, which many weighted ball programs do," Dodgers director of player developent Gabe Kapler said. "Our pitchers have responded admirably, and our coaches are enthusiastically supporting."
The Indians bought in full-sail long before Bauer and Kluber came on the scene, but those two are certainly the poster children for Cleveland's program. Take a walk through their Spring Training facility in Goodyear, Ariz., and you'll see thick, green pads hanging from the chain-link fences of the back fields and pitchers regularly thumping multicolored weighted balls into them. Callaway and Minor League pitching coordinator Ken Knutson say every Indians pitcher uses the weighted balls in some capacity.
In 15 years of using weighted balls, Knutson has never had a player say he didn't feel good using them. And the reason is very easy to imagine: Give a pitcher a 20-ounce baseball -- that's a pound and a quarter -- and have him shake it around, lift it over his head, mime his throwing motion for 15 or 20 seconds. Then put a baseball in his hand. It feels like a dart.
"You always get a smile, because the ball feels so light you feel like you can throw it 100 miles per hour," Knutson said. "And even if that's all you get out of weighted baseballs, I'm in."
The Indians, though, have had more success than that. After he began using weighted balls, Kluber saw the significant jump in velocity -- and his ability to sustain it as his innings wore on -- that led him to the 2014 AL Cy Young Award. In '16, Bauer, who struggled with command at the start of his career and has used underloaded balls to hone his accuracy, saw his walk rate per nine innings hit a career low and had a zone percentage (percentage of total pitches in the strike zone) well above the league average.
Stottlemyre, who tinkered with weighted balls while rehabbing a rotator cuff injury in the early 1970s, is surprised they haven't caught on in a bigger way.
"I believe in it," Stottlemyre said, "and I know one thing for a fact: If I was sitting in the bullpen with Mariano Rivera and I saw him using a weighted ball prior to all of his appearances, I would have me a weighted ball, too."
Lindsay Berra has covered a variety of sports, from baseball and hockey to tennis and the Olympics, since 1999. She joined MLB.com in 2013.