10 breakout players poised to repeat in 2019

Every year there are players who elevate their game to new heights. Sometimes it's the result of learning a new pitch or swing, while other times it's a byproduct of improved conditioning or more regular playing time. Some players simply improve with better luck, only to regress the following year.
Accordingly, it's not always easy to tell which breakouts are for real and which ones are flukes. By looking at the underlying numbers, however, one can identify which players actually got better. Here are 10 players who exceeded expectations in 2018 and are poised for additional success next year.
Jesús Aguilar, Brewers
On the heels of a promising 2017 in which he batted .265/.331/.505 with 16 homers in his first extended big league trial, Aguilar has broken through to become one of the National League's top sluggers in 2018. The 28-year-old has refined his approach at the plate by improving his walk rate from 8 percent to 10.8 percent and slicing his strikeout rate from 30.2 percent to 24.8 percent. Aguilar has also been able to tap into his power stroke by hitting more fly balls and pulling the ball more frequently. After ranking among the league leaders in hard-hit percentage in each of the past two seasons, Aguilar is primed to keep mashing in 2019.

Walker Buehler, Dodgers
After a cup of coffee as a September callup in 2017, Buehler began 2018 in the Minors, but was promoted in late April as a starter, tossing five scoreless innings against the Marlins in his first Major League start. On May 4 against the Padres, in just his third career start, Buehler contributed six hitless innings to the team's first combined no-hitter in franchise history. Buehler throws hard and with control -- two skills that should help him succeed going forward. The 24-year-old has dominated hitters with his upper-90s fastball and hard sinker, striking out more than a batter per inning in 2018. He has also displayed great command, yielding just 2.4 BB/9. The Dodgers have preserved his arm by keeping him under 100 pitches in all but four of his starts, so he should be ready to take on an increased workload in 2019.
Matt Chapman, A's
Since debuting in 2017, Chapman has rapidly emerged as one of baseball's best two-way players at the hot corner. In addition to providing Gold Glove-caliber defense, the 25-year-old has blossomed at the plate. After batting .234/.313/.472 as a rookie, Chapman has improved to .280/.363/.521 as a sophomore while helping lead the A's into contention. Chapman has chased fewer pitches outside the zone and swung at more pitches inside the zone this season, resulting in better quality contact and an improved BB/K ratio. Thanks to an increase in line drives, his hard-hit rate has jumped from 36 percent to 44.2 percent. He has also pulled the ball more frequently, enabling him to increase his ISO despite hitting fewer fly balls. With his slick glove and potent bat, Chapman has the potential to be Oakland's next Josh Donaldson.

Zach Eflin, Phillies
Eflin opened the year in Triple-A after struggling in his first two seasons, but when he returned to the Majors in May he was a different pitcher. The right-hander is throwing harder, averaging 94.6 mph with his heater -- considerably higher than his average four-seam fastball speed of 93.1 mph in 2017. His confidence in the pitch has skyrocketed, and it has accounted for more than 46 percent of his pitches after comprising less than a third of his offerings last year. His K/9 rate has soared to 8.5 and hitters have had much less success against him, batting just .263 after hitting .309 off him in 2017. Moreover, Eflin has continued to display solid control, issuing fewer than 2.5 free passes per nine innings. While Eflin's ERA is 4.42, his 3.86 FIP is evidence of what he might be capable of in 2019.
Mitch Haniger, Mariners
Haniger was on his way to a breakout in 2017 before injuries derailed his season, limiting him to just 96 games. His final numbers hinted at his promise, however, as he slashed .282/.352/.491 with 16 homers and 47 RBIs in only 369 official at-bats. Haniger stayed healthy this year, resulting in his first All-Star selection and career highs in many categories. He opened the season on fire with 10 homers, 27 RBIs and a 1.085 OPS in March/April and hasn't looked back, proving his strong performance in 2017 was legitimate. The 27-year-old has also displayed better discipline with a career-best 10.6 percent walk rate, as pitchers have come to respect his power. With an OPS above .800 in two straight seasons, Haniger is trending in the right direction heading into 2019.

Miles Mikolas, Cardinals
After three stellar seasons in Japan, Mikolas immediately excelled upon returning to the United States, winning his first six decisions en route to an All-Star nod. While his K/9 rate is just 6.2 -- mirroring his lifetime mark -- he has significantly lowered his home run rate while posting the lowest walk rate in the National League among qualified pitchers. Mikolas has relied less on his fastball and more on his breaking pitches to keep the ball on the ground, as more than half of the balls put in play against him have been grounders. That appears to be a recipe for success for the 30-year-old, whose improved control sets him up for continued success next season.
Max Muncy, Dodgers
Perhaps the most surprising contestant at this year's T-Mobile Home Run Derby was Muncy, who was released by the A's prior to the 2017 season and opened '18 in Triple-A. He got off to a hot start and was quickly called up, however, debuting as a pinch-hitter on April 17 and homering in his first start with the Dodgers the following day. It was a sign of things to come for the slugger, who became the fastest player to reach 20 homers in franchise history -- reaching the milestone in just 183 at-bats. He hits the ball as hard as anyone, leading the Majors in AB/HR ratio (min. 110 plate appearances) and ranking 12th in hard-hit percentage (min. 400 PAs). Muncy also has exceptional pitch-recognition skills, ranking behind only a handful of players with his 15.9 percent walk rate. As one of the game's strongest and most patient hitters, the 28-year-old appears poised to be a top power threat again next year.

Brandon Nimmo, Mets
Significant injuries to Yoenis Céspedes and Jay Bruce opened up consistent playing time for Nimmo, who has built on a solid 2017 by adding more power to his game, posting a .233 ISO (.158 in 2017). Said gains have stemmed from improvements in several areas, including hard-hit rate, fly-ball rate and pull percentage. Nimmo already had a high floor thanks to his stellar batting eye (career .385 OBP and 20.4 percent chase rate), but his added pop makes him more than just an on-base threat.
Nick Pivetta, Phillies
Despite flashing an impressive 9.5 K/9 rate as a rookie, Pivetta ended 2017 with a 6.02 ERA, a 1.51 WHIP and a 4.87 FIP. Using a more diverse pitch mix in 2018 that has featured more of his slider and curveball as well as a sinker, Pivetta has enjoyed increased success in his sophomore campaign (4.66 ERA, 1.30 WHIP, 3.66 FIP). In addition to allowing fewer homers and lowering his BB/9 rate from 3.9 to 2.7, he has posted one of the best K/9 rates among qualified hurlers at 10.7. Now that he's learned how to pitch instead of trying to throw it by everyone, the 25-year-old righty is primed for additional success in 2019.

Blake Snell, Rays
Like many young hurlers, Snell struggled to throw strikes consistently during his first two seasons, averaging 4.5 BB/9 and just over five innings per start. The hard-throwing lefty has put it all together in his third season, however, lowering his BB/9 rate (3.1) for the second straight year and posting the highest K/9 rate (10.7) of his career. The results have been staggering, as he was named to the All-Star team and owns one of the lowest ERAs (2.06) among qualified pitchers. With four quality pitches and improved command, the 25-year-old has the talent to be a perennial Cy Young candidate for years to come.