Boston's 'Core Four' hitting principles breeding prospect success

FORT MYERS, Fla. ¨C Boston was built to be a shining city on a hill, according to John Winthrop. Four centuries later, the Hub¡¯s top three baseball prospects are meant to be a shining example atop the Red Sox farm system.

Roman Anthony, Kristian Campbell and Marcelo Mayer ¨C the Nos. 2, 7 and 12 overall prospects entering 2025, according to MLB Pipeline ¨C are known colloquially as the Big Three in baseball circles in Boston and beyond, and it¡¯s the trio¡¯s willingness to buy into the Red Sox¡¯s hitting philosophy ¨C and their success in doing so ¨C that has set the standard for the rest of the hitters pushing their toward Fenway Park.

¡°When the best players are doing things, when they're as hard of workers as they are, when they are willing to fail as much as they are to get better,¡± said Red Sox senior director of player development Brian Abraham, ¡°I think it creates an environment, a culture that is one that players want to be in.¡±

To make it easy, think of it as the Big Three and the Core Four, the latter referencing the core principles the Red Sox instill in their prospects to become quality hitters: swing decisions, bat-to-ball skills, ball flight and bat speed.

The success of all three prospects relates in varying ways to those four standards. Anthony rose to the summit of the Top 100 with advanced swing decisions, loud exit velocities and a quick, whipping swing. Mayer has similar bat speed from the left side and has gotten stronger in pro ball but still puts the ball on the ground a bit too much.

But the success story to beat all success stories comes from Campbell, the 132nd overall pick in the 2023 Draft and MLB Pipeline¡¯s Breakout Prospect of the Year in his first full season. The story has been often-told, but the numbers are worth repeating. The former Georgia Tech star entered the pros with a propensity to hit groundballs but finished his first full season with a .330/.439/.558 line, 20 homers and 55 total extra-base hits over 115 games across High-A Greenville, Double-A Portland and Triple-A Worcester.

The root causes were two-fold: he was swinging harder than ever, and he was elevating on contact better than ever. Using heavy bats and other bat-speed practices, Campbell may have gotten so fast with his swing that it took some time to adjust to the new version of himself at the plate. He batted .216 last April but didn¡¯t post an average below .308 in any of the next four months.

¡°I think when you make some advancements in certain spaces, you have to get used to things, used to your bodies, the movement, used to the speed of the game,¡± Abraham said. ¡°I don't think we'd ever say someone swings the bat too fast. I can promise you that. I think it's more understanding what he's able to do physically, and then you know what he needs to do to have success day in and day out and balancing all those things out for that consistency.¡±

Campbell caught on quickly and is now in Major League camp as a serious contender to make Boston¡¯s Major League Opening Day roster, either at second base or in the outfield.

Reminder: he wasn¡¯t in the Red Sox preseason Top 30 prospects list this time last year. Seeing his rise ¨C and those of Anthony and Mayer -- and its direct connection to the Core Four principles has ripple effects from Worcester on down. There may be only one Kristian Campbell, but the role of the next Kristian Campbell is wide open.

¡°It's really easy to show that these guys have been working within our training environments and improved,¡± Abraham said. ¡°So if you do it, you'll be able to improve -- maybe not at the exact rate they have, but in similar ways.¡±

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Camp standout: Mikey Romero

Ask Abraham. Ask Alex Cora. Ask Campbell, even. The prospect garnering plenty of internal attention sits at No. 11 on Boston¡¯s preseason Top 30.

A first-round pick in 2022, Romero played only 112 games combined between his first two full seasons as he dealt with a stress fracture in his back. He was finally fully healthy in the latter half of the 2024 campaign and caught fire late, hitting .292/.326/.594 with 14 homers in 47 games between High-A Greenville and Double-A Portland.

With a full offseason to prepare, the left-handed-hitting middle infielder hasn¡¯t skipped a beat in limited Grapefruit League play, going 4-for-6 with a homer and a double while splitting time between short and second. He should be one to watch Thursday in the Spring Breakout matchup against the Rays in Port Charlotte.

¡°He¡¯s come in, physically, in the best shape of his career, swinging the bat fast and impacting the baseball,¡± Abraham said.

For more on Romero¡¯s big spring, check out Ian Browne¡¯s newsletter.

Breakout candidate: Nelly Taylor

Taylor (No. 21) was a lower pick than Campbell in the 2023 Draft, going in the 11th round (though he signed for above slot at $300,000), and he came out of the junior-college ranks. In other words, he might have needed a little more experience in pro ball to truly jump. He hit .228/.336/.358 with six homers in 101 games with Single-A Salem in 2024 and ended the season on a high by going 11-for-38 (.289) with five extra-base hits in 10 High-A games after a late-August promotion.

Like Campbell, the former Florida State commit is at least a plus runner, giving him one major avenue to be valuable, and he¡¯s gotten stronger under the Red Sox¡¯s guidance. But another year of hitting instruction could mean he¡¯s ready to pop as a left-handed slugger.

¡°We've improved some of his ball flight qualities and his bat speed,¡± Abraham said. ¡°I think that will give him the opportunity to have the success that someone like Kristian had. Certainly the meteoric rise that Kristian had is unique for sure, but I think of him as guy that can be really interesting.¡±

Something new: Connelly Early

Moving to the pitching side, Early (No. 10) seemed like the poster child for the Boston pitching philosophy of only throwing your best stuff. If you don¡¯t have a quality four-seam fastball, don¡¯t throw it. For example, Worcester pitchers threw four-seamers 16.2 percent of the time in 2024, lowest by far among Triple-A pitching staffs.

The 2023 fifth-rounder, who sat just 92-94 mph with his heater last year, instead showed a pair of solid breaking balls in his curveball and slider, and his low-80s changeup earned plus grades for its separation and movement. Relying on the depth of that arsenal, he posted a 3.99 ERA and 138 strikeouts in 103 2/3 innings between High-A and Double-A in his first full season.

Come this spring, however, he¡¯s already been up to 97 mph in his first live throwing session after making adding velocity an offseason priority. The quality of his other stuff means Early still doesn¡¯t need to lean on the fastball to dominate hitters, but being able to blow it by them opens up more possibilities as he heads back to the upper Minors.

¡°When all of a sudden you have a guy who's 92-94 throw 97, that's a significant change,¡± Abraham said. ¡°It allows the entire arsenal to play up significantly.¡±