In an era obsessed with spin rate, Cubs reliever Dillon Maples is a king.

Over each of the last two seasons, the spin on his four-seam fastball has been tops in the league. Last year in his small sample of 11.2 innings at the major league level, the pitch spun at 2,889 rotations per minute (RPM) on average, roughly 150 more RPM than the second highest-spun fastball in baseball. 

Despite this otherworldly skill, Maples has struggled to find consistent success in the major leagues. In three stints with the Cubs between 2017 and 2019, he posted an impressive 35% strikeout rate, but he walked nearly 20% of the batters he faced with an ERA above 8.00.

The underlying metrics on Maples’ “stuff” make him a true anomaly. He easily averages above 96 mph on his fastball, touching over 99 last season with his outlier spin rate. His slider is his strongest breaking ball with high usage. With further development and improved command, he could become a high-leverage reliever and an option for the Cubs’ expanded roster in the event of a 2020 season.

The Cubs drafted Maples in the 14th round of the 2011 MLB June Amateur Draft out of Pinecrest High School in North Carolina. For the next four seasons, Maples shuffled between Rookie Level, Class A Short Season and full-season Class A.

It wasn’t until 2017 that he began posting his signature gaudy strikeout rates. He struck out 34% of the batters he faced in 31.1 innings with High-A before jumping his strikeout rate to 43% after a promotion to Double-A. His bat-missing abilities earned him a promotion to Triple-A and moments later he debuted in the major leagues on September 3, 2017, just five months after starting the season at High-A. Aside from one rocky outing, Maples finished 2017 strong, striking out 9 of the final 17 batters he faced that season.

His major league stints in 2018 and 2019 were a mixture of dominant stretches and getting beat by the home run ball. The only two appearances where he allowed an earned run in the majors during 2018 also featured home runs. In 2019, he pitched well in his first eight major league outings before relinquishing 2 or more earned runs in three consecutive appearances. In his final 2.1 innings of 2019, he didn’t walk a batter or allow an earned run. 

To understand why Maples’ four-seam spin rate doesn’t guarantee success requires an understanding of not only spin rate, but spin direction, spin efficiency and a variety of other measurements. In the interest of simplicity, spin efficiency alone can help give context to Maples’ repertoire. As popular baseball physicist Alan Nathan puts it, “For a given total spin rate, a larger spin efficiency means more movement.” 

Maples’ four-seam fastball had a spin efficiency near 50% in 2019, bottom 2% in the league. The best fastballs in the league have high efficiencies (98% or higher), allowing them to resist the effects of gravity and drop less than a hitter expects. This results in greater vertical movement of the pitch. The sheer velocity of his fastball has allowed him to get a lot of hitters out, but metrics like Maples’ lack of spin efficiency signal the pitch could be even more productive.

Fixing Maples’ spin efficiency, however, isn’t a simple task. Some pitchers are comfortable with a certain grip, release or arm action that creates the lower efficiency. Others can tweak variables in controlled settings but lose their improvements in game situations. 

In 2019, Maples opted to use his slider more and his fastball away from the top of the zone, as he told The Athletic early in 2019. His usage data from 2019 backs this up. He turned to his slider nearly 60% of the time and his fastball was scattered all over the plate. This spring, Maples gave thought in the Cubs “Pitch Lab” to altering his wrist position at ball release to adjust his fastball’s spin efficiency and improve its vertical movement. In just two 2020 spring games, he struck out 3 batters and walked only 1, without allowing an earned run — small signs of potential progress. 

A tweak nearly invisible to the casual viewer can be a massive stepping stone for Maples’ career if his fastball adjustments stick come a potential 2020 season. This more efficient fastball could even make his slider better, creating a two-pitch nightmare for hitters out of the Cubs bullpen. With the potential for additional roster spots, this slightly modified Maples could be a key bullpen piece to solidify the Cubs competitiveness in the NL Central.