Theo Gillen Is Primed for a Breakout in 2026

Over the past few draft classes, the Tampa Bay Rays have been obsessed with high school talent. Since 2020, seven of the Rays’ last nine first-round picks have all been picked out of high school, and this model has repeatedly served them very well.

The Rays’ player development has hit big on some of these players, with Carson Williams and Xavier Isaac sitting at the top of this group. They’ve constantly been able to maximize these players and truly get the very most out of their raw tools.

However, the Rays’ next big win could come in the shape of their 2024 first-round pick, Theo Gillen. He performed well during his first full season of professional baseball in 2025, but there’s room for even more growth. This speaks volumes to his game, as he’s already become our No. 89 overall prospect in baseball.

Gillen has one of the more interesting raw profiles among recent high school draft picks, and his play style is the exact model the Rays consistently develop into stars. If they can keep building on the tools he’s already showcased in his first full year of professional baseball, he could quickly join Williams and Isaac as two of their biggest hits in the first round.

Let’s dive into his game and take a closer look at why 2026 could be the year Gillen truly breaks out.

Theo Gillen’s 2025 Success

After kicking off his professional career with an eight-game stint in Low-A during the 2024 season, Gillen returned to the level, looking to do some serious damage last year. He did all of that and more, simply tearing the cover off the baseball at every opportunity he was given.

Across the 73 games he played, Gillen slashed .267/.433/.387 with five homers, 36 stolen bases, and an astounding 151 wRC+. As if this wasn’t impressive enough, Gillen showcased a very good eye at the dish, as he managed to post a walk rate of almost 20% during this span as well.

Digging a little deeper, Gillen’s patience allowed him to force pitchers to attack him in the zone, which quickly became a recipe for success. He posted a contact rate just shy of 75%, which gave him the ability to do damage on the strikes he saw.

Still just 19 years old, the approach Gillen showcased this season was well beyond his years, as this type of production from a teenager is hard to come by. In fact, among prospects with at least 300 plate appearances, only four teenagers posted a wRC+ above Gillen’s mark of 151, which places him among elite company.

Aside from his tools at the plate, Gillen’s speed is one of the most underrated aspects of his offensive game. Only 21 teenagers with at least 300 plate appearances managed to steal 35 or more bases, and Gillen was a part of this group.

The biggest issue Gillen faced during the 2025 season was his struggles to stay on the field and remain healthy. He had three separate stints on the injured list, which kept him from getting significant playing time.

The battle to stay healthy isn’t new for Gillen, as he’s been sidelined numerous times since his high school career. For example, he had surgery to repair a torn labrum during his sophomore year, and a knee injury held him back the very next season.

All things considered, the 2025 season was a huge win for both Gillen and the Rays. Although he struggled to stay on the field at times, Gillen was one of the better pure hitters in the minors when he was healthy. He’ll be a name to keep a close eye on if he can carry this production into 2026.

Evaluating the Raw Tools

Aside from his impressive on-field production during the 2025 season, the most exciting part of Gillen’s game are his raw tools. He’s already a very well-rounded and fairly polished player, which isn’t something to take lightly given his age.

For starters, Gillen has a very smooth, direct swing that allows him to extend his hands through the baseball. This type of swing has allowed him to be one of the better bat-to-ball hitters in the minor leagues, and it earned him positive hit-tool grades across most major outlets.

With Gillen still being just 19 years old, there’s still room to dream on his offensive profile. He’s already flashed decent raw power, but he has yet to put it together over a full season. His upper and lower halves seem out of sync at times as well, which, if corrected, could finally lead him toward more extra-base hits.

As I previously mentioned, his best ability to this point has been his plate discipline. He put up a 13% chase rate this season in Low-A, rarely expanding the zone. When paired with his 19.8% walk rate, Gillen’s patience becomes a highlight of his game. With pitchers unable to make him expand the strike zone, he’ll have more opportunities to do damage.

In addition to an intriguing offensive profile, there’s a lot to like with his glove as well. The Rays transitioned Gillen from shortstop to center field immediately after selecting him in the first round, and he’s handled it fairly well so far. The Rays are betting on his athleticism with this move, and he’ll get even more comfortable with more reps at the position.

It’s easy to see why the Rays trusted his athleticism enough to make this move, though. To say the least, Gillen is quick on the bases. His speed has been graded out in the 60s from multiple outlets, including Aram Leighton in Just Baseball’s Top 100 list.

This speed gives him immediate upside in center field due to the ground he can cover, and it’s already translated well to the bases. If he had played a full 162-game season at the pace he swiped bags in 2025, he would’ve been on pace for nearly 80 steals.

Overall, while he’s far from a complete prospect, Gillen’s raw tools show a lot of promise as he continues to develop. If he’s able to keep growing and sync up his swing a little better, he could quickly become a household name in the minor leagues.

Where Can Gillen Improve in 2026?

Now that we’ve taken a look at Gillen’s on-field production and his raw tools, we can look ahead to where he can make strides in 2026. The ceiling is undeniably high, but like any young player, there are areas where he can refine his game and unlock even more potential.

The most important hurdle for Gillen to tackle in 2026 is simple: health. His injury history has plagued him since his high school days, and while he’s shown flashes of excellence while on the field, he has yet to put it together for more than 73 games.

It’ll be crucial for Gillen to stay on the field, especially as he transitions to a new position and likely makes the jump to the High-A level. If he’s able to get consistent reps for a whole season, it would do wonders for his development.

While Gillen’s hit tool and plate discipline are already at a high level, his raw power still has some untapped potential. In 2025, he showed flashes of taking that next step forward with his power, but it ended there.

If Gillen can continue to refine his swing so that his upper and lower halves work together a little better, his power could find more consistent results in 2026. His power will likely be capped due to his frame, but there’s definitely still room for growth.

Defensively, Gillen still has room for improvement as well. While moving from shortstop to center field was no easy task, the 19-year-old already showcased flashes of being able to track down balls in the gap, but he occasionally struggled to do the little things that career center fielders do naturally.

A lot of Gillen’s potential improvement in center field relies simply on him getting more reps at the position, which is another reason he must stay healthy in 2026. With more time in center field, he’ll have more chances to refine his defensive game.

2026 will be a massive year for Theo Gillen, as he’s potentially just a few steps away from taking that leap into prospect stardom. If he’s able to stay healthy, improve his power, and improve defensively, we could be looking at the next success from the Rays’ player development.