Jesús Aguilar Has Transformed Himself at the Plate

First base is an offense-first position. Sure, it’s great to have a first baseman who is handy with the glove and can scoop errant throws, but by and large, it’s a position for sluggers. Even though the position supplied both of last season’s MVPs — Freddie Freeman and José Abreu — it’s production doesn’t hold up as strongly as it has compared to previous years. From 2018 through the 2021 season thus far, first basemen have averaged a 108 wRC+ compared to an average wRC+ of 115 over the 2000-17 seasons.

There are plenty of teams suffering from lackluster production at first base but I want to highlight two of them: the Milwaukee Brewers and the Tampa Bay Rays. The Brewers have managed a measly 68 wRC+ and -0.5 WAR, with contributions mostly from the duo of Keston Hiura (who is now in Triple-A) and Daniel Vogelbach. The Rays have been a bit better with a wRC+ of 82 and -0.1 WAR. These aren’t the worst teams in the majors at first base but they do share something in common; they once had Jesús Aguilar under team control and let him go.

In his tenure with the Marlins after being selected off waivers on December 2, 2019, Aguilar has solidified himself as the team’s primary first baseman, slashing .254/.356/.469 with 14 homers across his two seasons (the stats in this piece are through May 9); that’s good for 126 wRC+ and 1.2 WAR. This season has been particularly good to Aguilar so far. He’s slashing .269/.363/.490 and is in the top 10 in the majors among first basemen in wRC+ (9th) and WAR (9th). Not bad for a waiver pickup! I make mention of his previous clubs’ oversight not to shame them; it’s not the first time a valuable player has been overlooked. But his path to the player he is today is a unique one.

Aguilar’s departures from Milwaukee and Tampa Bay were warranted if you view his performance a certain way. He began the 2019 season as a Brewer and drastically underperformed after a breakout season in 2018 where he slugged 35 home runs and was an All-Star, posting above average exit velocity, barrel rate (86th percentile), and hard hit rate (75th percentile) accompanied by a high strikeout rate. Things changed quickly, however. In 222 plate appearances for Milwaukee in ‘19, he experienced a significant drop in ISO from .264 to .149 largely due to decreased launch angle (13.7 down from 16.2) and fly ball rate (37.9 from 40.9). As a team competing for a division title, Milwaukee didn’t show much patience for Aguilar to return to form and shipped him off to Tampa Bay for RHP Jake Faria. In limited time for the Rays, Aguilar produced average numbers at the plate and was ultimately DFA’d.

Aguilar has made an impressive turnaround but it hasn’t happened overnight. Over the course of his five seasons as a big league regular player, he has made steady progress in his plate discipline, which is difficult for most major leaguers to do. As a rookie with Cleveland in 2017, he finished the season with a respectable 114 wRC+ in 331 plate appearances despite a below average walk rate of 8.0% and a strikeout rate north of 30%. Amazingly he has been able to reduce his strikeout rate in each of the following four seasons, something no other big leaguer has accomplished during that time. Only two other active major leaguers have managed to bring their K% below 20% after posting a prior season finishing with a K% of at least 30%: Randal Grichuk and Trevor Story.

What makes this even more impressive is that league-wide rates have been going the opposite direction. Aguilar is striking out at a rate of 16.1% so far this season, nearly half of his 2017 season average. Meanwhile, the league-wide rate has gone from 21.6% to 24.3% over that stretch. He’s done this by improving his contact rate, particularly in the zone, where over the past two seasons he’s averaged a Z-Contact% of 89.4% which is more than 10% better than in 2017. This season that has been complemented by an increased Zone% (pitches he sees in the zone), which has helped him get off to a solid start.

He’s made a similarly impressive adaptation at the plate when it comes to drawing walks thanks to a more patient approach. While these changes aren’t as apparent as his contact rates, Aguilar’s swing rate has declined from 2017-18 both in and out of the zone, with the exception of the shortened season in 2020. Combine the added patience and more consistent contact and you get a swinging strike rate, the bugaboo of many of today’s major league hitters, of exactly 10%. Exercising patience has been paying off. He’s walking at a career best rate of 12.9%. He’s outpacing his ZiPS projections by a large margin, which had him regressing from 2020 in both walk and strikeout rate. He’s currently sitting with a BB/K ratio of 0.80, which is eighth in the majors among qualified first basemen and nearly twice the ZiPS projected BB/K of 0.45.

Signs of Aguilar’s improvement were evident in 2019, but it’s easy to understand why his gains in plate discipline were overlooked: the step backward in the power department outweighed his improved patience and approach. Aguilar did rebound a bit after being traded to the Rays, but some of his peripherals were of concern. His hard hit rate decreased from 42.6% to 37.4% and his barrel rate plummeted from 10.9% to 6.6%. These rates, however, can overstate a hitters’ ability to hit the ball hard. Both measures use batted ball events (BBE) rather than plate appearances as the denominator. This means that strikeouts and walks are not factored into the calculation. It’s possible that a player who is improving his contact rate can experience a drop in hard hit rate but still end up with the same amount of hard hits over the course of a season. In the case of Aguilar, because he’s been able to strike out less, he can sustain a drop in hard hit rate but still find success at the plate.

Sure, Aguilar’s power numbers have indeed decreased. But the drop in power is not nearly as great as it appears just looking at HardHit% and Barrel%. If his numbers hold up, this season will be Aguilar’s best by wOBA and wRC+ despite career lows in HardHit% and Barrel%.

Last week, I wrote about how the high fastball is the main driver behind the increase in strikeouts this season. This is another area where Aguilar zigs while the rest of baseball zags. To recap, fastballs are generally being thrown at higher velocities and with higher spin rates year-over-year. As a result, hitters’ swinging strike rates on fastballs in the top of the zone have gone up. But unlike most, Aguilar has gotten better each season at hitting fastballs in the top of the zone.

As a testament to Aguilar’s focus on improved contact, here’s a clip of him depositing a top shelf heater from Jacob deGrom into the left field bleachers last season, something few players can claim (although teammate Jazz Chisholm Jr. accomplished this feat earlier in the year, as chronicled here by Justin Choi).

It’s early in the season and Aguilar’s numbers will probably regress a bit, but he’s finally bringing back the power he showed in 2018 to pair with his growing affinity for drawing walks and making contact. His fly ball rate is sitting at 43.7%, the highest of his career, with an average launch angle of 14.3 degrees. He knows that it’s his job to hit for power, but patience at the plate remains a priority to him. Aguilar was quoted recently in the Miami Herald stating:

“I’m just trying not to be overly aggressive at the plate. It’s been hard, especially for me. I’m supposed to be a home-run hitter. Things are happening like they’re supposed to happen. … We’ve just got to keep going.”

For the Brewers and Rays, two analytically-driven teams with a real need at first base, it must be difficult to see the success that Aguilar is having in Miami knowing that he could be suiting up in their uniform. It’s doubtful that Aguilar can keep up his current slugging percentage of .490; his previous seasons suggest that he’s enjoying the better end of a small sample and will regress in fly ball rate. But I wouldn’t bet against him maintaining his BB% and K% gains. He’s got the history now to prove it’s not a fluke.