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Javier Baez is in a baserunning slump. Last Friday, he was caught stealing third base for the final out of the fourth inning—with a 3-0 count on a left-handed batter, and Baez representing the tying run. It was a boneheaded play, though Baez has earned some leniency in such cases this year. It was also his third time being caught stealing since the All-Star break, and on Monday night, he was picked off of first base and caught again, giving him more times caught than successful thefts in the second half.

He’s also been thrown out a couple times in the last two weeks on other baserunning plays, trying to force the issue and take the extra base when it just wasn’t there. Monday night, Cubs manager Joe Maddon talked about seeing fatigue in Baez, and about looking for a chance to get him some rest. He’s right: Baez played in all but two of the Cubs’ first 130 games before getting Wednesday off, and it’s showing. He’s not quite as sharp in his approach or his decision-making, and he’s perhaps a half-step slower than he was during the early summer.

Of course, just before this slump, Baez was on the best baserunning hot streak the league has seen in years. Before being nabbed in a game in San Diego just before the break, he stole 16 bases without being caught, over a span of two-and-a-half months. Two of those steals were of home plate, and he led baseball in steals of third base. He had three triples and at least that many hustle doubles during that stretch, many of them punctuated by acrobatic slides to avoid a last-second tag. For two months, Baez took every possible opportunity to run, and (quite apart from throwing him out) teams often gave him an extra base by throwing the ball away or making a mental error.

This isn’t a normal way to talk about baseball players. We all recognize that players have streaks and slumps at the plate, and careful observers sometimes note that fielders similarly fluctuate. Hardly anyone has a true baserunning hot streak, though—not merely a long time without being thrown out, because that can be borne of good instincts and cautious decision-making, but a full-on hot streak complete with dazzling plays and lucky breaks, the kind of thing that drives opponents crazy. Yet, there’s no other way to properly convey what happened whenever Baez took the field during that period.

It’s just another way in which Baez is changing our understanding of what a ballplayer can do, about how they can separate themselves and how they contribute to wins. By now, virtually any reader of these words is likely familiar with Baez’s tagging prowess around second or third base, for which he first got famous two years ago. The only player one might plausibly prefer as either a tagger on an attempted steal or the middle man in a relay to third base or the plate is Andrelton Simmons. The value of Baez’s power bat and sterling glovework are obvious, but Baez is better at adding value in non-obvious ways than almost any other player in baseball.

This season, Baez is making history in still another way. He’s up to 41 games played at shortstop, in addition to the 94 he logged at second base. By the end of the season, Baez will likely eclipse 50 games at shortstop, marking the second straight season in which he’s qualified for the batting title while playing at least 50 games at each middle-infield position. The only other player to do so since World War II was Boston’s Jody Reed, in 1989 and 1990. Reed drew some walks and hit for enough average to be an above-average player, despite a lack of impressive power or speed. He was a shortstop when he first arrived in the majors, but slid off the position over a two-year span, making history for his versatility almost by accident.

Unlike Reed, Baez has started each of the last two campaigns at second base, and has played shortstop down the stretch. It’s not quite fair to say that he’s moving back to that position; each move has been partially necessitated by injuries and ineffectiveness that have plagued Addison Russell. Still, he’s more than holding a place. Fielding Runs Above Average grades Baez slightly below average; both of the other major defensive metrics rate him slightly above average. He’s truly a multi-positional defensive weapon, the most flexible everyday infielder since Marco Scutaro and Craig Counsell’s brief stints as regulars, and the best hitter ever to be asked to do what he’s doing. (The current record for OPS by a player who played 50 or more games on each side of the keystone is .803, by Jimmy Johnston of the 1923 Brooklyn Dodgers.)

Maddon has often talked about putting Baez wherever he thought the ball was likely to go most frequently during a given game—essentially, saying that he would give Baez the largest possible defensive responsibility, whenever circumstances allowed it. In 2016, Baez played 59 games at second base, 62 at third base, and 25 at shortstop, because (with Ben Zobrist and Addison Russell fully healthy and effective, and the outfield depleted by injuries and ineffectiveness) he was needed most at third base. Eighteen of his 36 starts there that year came when Jon Lester was on the mound, because opponents would stack their lineup with righties to counter Lester, so most ground balls went to the left side.

This season, Baez has mostly shored up the middle infield, but he’s made 13 starts at third base, including six behind Lester and four behind Cole Hamels—the first four starts Hamels made in a Cubs uniform. His steadying presence on defense helped Hamels start his Chicago tenure better than any other pitcher traded midseason has ever done with their new club. Being able to slide a hitter as gifted as Baez all over the infield has altered the Cubs’ season radically. It helped them paper over the prolonged absence of Kris Bryant. It facilitated their acquisition of Daniel Murphy. However, this year, it’s also meant having one of the best offensive shortstops in the history of the game. That deserves a bit more discussion, because given where Baez was when he entered the league (and even given where he was perhaps a year ago), it’s shocking to see how far he’s come at the plate.

He’s made significant changes, and they’ve helped him unlock his potential as a full-fledged superstar. First, let’s establish just what a level Baez is reaching right now. Since 1947, here are all of the players with at least 40 games at shortstop while posting an OPS of .900 or greater, at age 25 or younger: Alex Rodriguez (five times), Hanley Ramirez (three times), Troy Tulowitzki and Nomar Garciaparra (twice each), Derek Jeter, and Ernie Banks. If the season ended today, Baez and Manny Machado would both join that list. That’s staggering, especially given that Baez doesn’t draw enough walks to inflate his on-base percentage. He’s getting into historic territory—not just hitting at a level few hitters at any position can match this year, but doing it at the most important defensive position on the diamond—by hitting the ball hard, and doing it often.

The success Baez has found at the plate this year is rooted, essentially, in aggressiveness. He’s swinging at the first pitch nearly half the time this season—up from just over a third of the time last year. Of all the pitches he’s seen within the strike zone, Baez has swung at 78.7 percent this year, giving him a higher Attack Rate—I’m making this name up, but in today’s game, it’s important to think of it this way; swinging very aggressively within the zone is a valuable trait, just as much as laying off pitches outside the zone is—than all but one (Freddie Freeman) of the other 164 qualifying hitters this season.

This isn’t about gaining a newfound feel for the zone; Baez also swings more often at pitches outside the zone than anyone but Corey Dickerson and Salvador Perez. As he’s gotten more aggressive, however, Baez hasn’t traded anything away. He’s making contact more often, both in and outside the zone. He’s hitting fewer ground balls and fewer pop-ups, driving the ball to center and right field much more often, and generating hard contact on a higher percentage of his batted balls. He hasn’t had to get worse at anything in order to get better at other things, because a major adjustment to his mechanics has allowed him to access his physical gifts in a way he never could before.

Last season, Baez had two different swings. With zero or one strike against him, he employed a fairly significant leg kick. If and when the count reached two strikes, he switched to a quicker, shorter motion, with only a minimal leg lift. In both swings, however, there was a common initial movement with his hands: up, and back. Baez had a pronounced bat wrap, one that forced his hands to play catch-up with his lower half. It’s the kind of movement you hear about mostly in prospects, because hardly anyone can get away with it in the majors. It takes lightning-fast hands and exceptional hand-eye coordination to deliver the barrel consistently to the baseball that way, and even then, one must build the other elements of one’s swing—especially the timing of the lower half—around that movement.

That’s what Baez was doing: getting his foot down early, then twisting furiously through the zone, trying to manipulate his bat path to generate a bit of loft on the way. It’s a testament to Baez’s sheer talent that he hit productively that way, even granting that he’d quieted it down significantly since entering the majors even by last season. Nonetheless, it was a bad habit. Baez isn’t just blessed with bat speed. This year, he’s more upright in the batter’s box, and a bit further off the plate. He’s using a higher leg kick, and waiting a few milliseconds longer to get his foot down. When he gets to two strikes, he doesn’t go into emergency mode: the stride stays.

His hands start a bit farther from his shoulder, and instead of starting with a counter-movement that forces him to rush the bat into the hitting zone, he uses a cocking of the bat that gets his hands moving and begins to put his barrel on the plane of the incoming pitch. His hands are farther from his body throughout his swing, which increases the speed of his barrel without demanding that he actually swing harder. Using his lower half much better makes him better able to adapt, and gives him the ability to use his hand-eye coordination more productively. Despite eliminating that two-strike swing, Baez isn’t down to one swing: he’s up to whatever number of swings matches the number of pitches opponents might use to try to get him out.

Without doing it in the classical fashion (by becoming more patient or trading power for consistent contact), Baez has become an extraordinarily smart hitter. He’s having a season for the ages because he’s figured out an entirely new way to use the most exceptional tool in his box. This is his budding legacy: to play in a way that suggests everything but subtlety, yet derive tremendous value from subtle things; to carry himself with such confidence that he appears selfish, yet transform his team through selflessness; and to play with such fearlessness that outsiders regard him as stupid, yet win games with his intellect.

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If Baez swings at a high percentage of pitches in the zone, and a high percentage of those out of the zone, one would think he'd been near the very top of the list of batters swinging at all pitches, balls or strikes. Since he's good at making contact, that would explain the dearth of walks.