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A deep dive into Adalberto Mondesi’s 2018 season

An in depth analysis of Mondesi’s season

MLB: Cleveland Indians at Kansas City Royals Denny Medley-USA TODAY Sports

With the 2018 season in the book (for the Royals at least), everything went as expected. The Royals lost 104 games, Whit Merrifield put up 5-wins, and Adalberto Mondesi was worth almost 3-wins himself. Wait...okay, none of that was expected, maybe Mondesi’s output the least expected.

After looking miserable at the plate in 2016 and 2017, Mondesi got the call again in 2018 and put together a very strong performance after the Royals decided to move on from Alcides Escobar 1,800 plate appearances too late. Mondesi posted 2.8 fWAR on the back of a 114 wRC+ and +5.1 baserunning and fielding, doing so in a little under half a season.

The big question next year is what will his numbers be like? His PECOTA/ZiPS/Steamer projections are going to be a big point of argument this winter, likely on the back of what will almost certainly be underwhelming numbers to some. So in that vein, let’s take a deep dive at his 2018 season and talk about what next season and the future could be like.

The Bull Case

When making the bull case, you can simply point to his age and performance as indicators towards the future. In the history of baseball, ~230 players all time have posted 2.8+ wins at the age of 22. That number might not be impressive on the surface, but there have been 1,172 age-22 seasons (min. 150 PA) in baseball history, meaning Mondesi is in the top 20% or so of all those seasons. When it comes to just shortstops, only ~40 players have had better age-22 seasons than him (a similar 20% overall).

His .222 ISO is the 4th highest ISO by a 22-year old SS in history, just shy of Juan Uribe (.223), Carlos Correa (.235), and Alex Rodriguez (.249). He’s almost 20 points ahead of Corey Seager’s age-22 season.

Mondesi also stole 32 bases in just 291 plate appearances, the 9th best age-22 SB/PA of all time.

Using the sum of z-score method, here are the closet age-22 seasons to Mondesi (prorated to 600 PA - a dangerous extrapolation but just for our purposes here) based on wRC+ (no per 600 PA needed), defense, baserunning, and fWAR:

Outside of Byron Buxton (which we’ll get to in a minute), the lowest WAR for a similar age-22 player is Colby Rasmu at 18.3. The next closest is Fred Merkle (25.7), and Elvis Andrus (26.9). From then on it starts to skyrocket up to Bill Dahlen and his 77.5 career WAR.

That list has several current or recent stars on it: Evan Longoria, Mookie Betts, Elvis Andrus, and Hanley Ramirez. Even the “worst” non-Buxton career on there (Rasmus) would still be a wild success for Mondesi.

Simply put, player who post 3+ wins (2.8 for Mondesi technically) at age-22 generally do pretty good.

75% of these players are at or above 20 career WAR

It’s easy to dream on the speed, above average defense, and the power he’s gotten too. Let your dreams run wild and turn him into a perennial 5+ win player and the best shortstop in Royals history.

Diving into the deeper realm of stats (courtesy of Andrew Perpetua’s, Mondesi’s batting average on contact (BACON) was .385, amongst the top 20 in the league, near names like Freddie Freeman, Giancarlo Stanton, and wunderkind Juan Soto. His Value Hits% (a measurement of objective parameters to classify high quality hits - akin to barrels with Statcast, though Statcast is spray agnostic while xStats considers it) ranks in the top 40, near players like Justin Upton, Kris Bryant, Matt Olson, and Jose Abreu. Mondesi also did fairly well on High Drive%, finishing in the top 40 of hitters out of 355 to receive at least 200 plate appearances.

Back in August, I pointed out on Twitter than Mondesi may be fixing his approach a bit at the plate:

A week or so ago, Jeff Sullivan of FanGraphs noticed the same thing and covered it a bit at the site

As Mondesi reached the majors again this season, he was hitting the ball with far greater authority. He also became considerably more aggressive swinging at would-be strikes. As Mondesi has received more regular playing time down the stretch, he’s maintained his batted-ball authority, and he’s maintained much of his in-zone aggressiveness, but you also see a sharp downturn in chases. Mondesi has still been going out of the zone more often than average, but of late, his numbers look a lot more reasonable. He’s not just a hacker. He’s not just a talented hitter who doesn’t have any idea. He’ll never be confused for Joey Votto, but Mondesi is swinging both better and smarter.

A lot going for Mondesi, despite his flaws, is that he’s young, has hit for power, has used his speed, and is a good defender. That’s four out of five tools, with some argument that the fifth tool (hit tool) has made some improvement. That’s really the bull case, that Mondesi has been good despite his flaws, and it’s not unreasonable to expect him to improve, meaning he’ll be even better on a skill level; not just more of the same combined with more playing time. There’s a danger in extrapolating small sample sizes, but it’s not as if Mondesi is coming out of nowhere. He was a top 20 or so prospect with a decent floor likely. Him turning it on should shock no one.

The Bear Case

If the bull case is made off of looking at the high level data (with some xStats thrown in), then the bear case can be made mostly off of his peripherals. I don’t mean for the point of this piece to be me taking a side, but I think I lean more towards the bear case than the bull. Not that Mondesi can’t be a useful player, but I think there are significant underlying issues that need to be fixed. I’m not saying he can’t fix them, I’m just saying if they don’t get fixed there is an unbeatable problem.

Walk Rate/OBP

Probably the main thesis for the bear case here. Mondesi ran one of the lowest walk rates in the majors, coming in a just under 4%. His OBP (.306) didn’t come in quite as low in the league (league average .323) but it was boosted by his BABIP and power.

Amongst his walk rate peers, Mondesi hit for the best power, the highest wRC+, and had the second highest BABIP.


It’s a bit easy to point to BABIP as the cause of regression for a player. Mondesi didn’t have an unruly BABIP (.341) but it was still 45 points above the league average. Players can run higher BABIP really through two methods: be very fast and/or hit a lot of line drives. Mondesi is certainly fast, so there is a connection that he could potentially run a higher BABIP than normal. This however is accomplished by infield hits and bunting (when it comes to speed), neither of which Mondesi really did an incredible amount of. His infield hit% was just outside the top 40 and his bunt hit% was in the back end of hitters with at least one bunt base hit (97th out of 123 hitters - excluding pitchers). There probably isn’t much regression coming (Mondesi ran a league average line drive% too) but you could make the case that his BABIP might be 20ish points lower. xStats pegged his expected BABIP (xBABIP) at .322.


As noticed in the walk rate table above, Mondesi had a strikeout rate of 26.5%. That in and of itself isn’t a death sentence or anything (Aaron Judge almost won MVP with a 30% rate), but it is often better paid with either a high walk rate (not a strength of Mondesi’s clearly) or a lot of power. If Mondesi keeps hitting for a .200+ ISO, then he can make the 26.5% strikeout rate work. If you think Mondesi is more likely to hit for the same power he did in the minors (~.152 ISO) then the strikeout rate won’t work. It’s worth noting here that we’ve seen player hit for more power in the majors due to the “juiced” ball (though the de-juicing of it may have begun).

Plate Discipline

His strikeouts are tied to his suboptimal plate discipline numbers; a catchall term not strictly only referring to solely what he swings at but what happens when he swings too. This is really where the crux of the bear argument begins, as his low-OBP and high strikeout rate stem off his plate approach issues.

Mondesi swings more than most players in the league, but he makes contact at one of the lowest rates in the league. His inability to make contact is made worse by his approach, swinging at a little more than half the pitches he sees.

Maybe we can look at this another way, and look at his swing rate peers vs their contact rate:

Those are players with similar swinging numbers (outside, in the zone, and overall) as Mondesi and then their respective contact data. Mondesi by far has the lowest contact rate and the highest swinging strike rate. His zone contact% is similar to David Dahl and Scott Schebler, but those two make a lot more contact outside the zone. Nick Hundley is a bit of the opposite; similar out of zone but different in zone.

Now let’s sort it by the opposite, looking at his contact rate peers:

*a note here: having a high z-swing% isn’t necessarily good/bad and it depends upon ability to make contact, power, and overall plate approach. For these purposes, we are trying to outline free swingers, so a high z-swing% is treated as “bad”

The top and bottom player on the table (Mondesi and Judge) almost couldn’t be more dissimilar when it comes to deciding which pitch to swing at despite being very similar to what happens when they do swing. Judge rarely swing, and while he does have contact issues, he gets away with it by being very selective. Mondesi is most similar to Daniel Palka, Avisail Garcia, and John Hicks from a contact perspective.

Now there is always the case that Mondesi could fine tune his approach as he gets better. It’s certainly happened before. He wouldn’t be the first player to do it. Hell, Eric Thames basically taught himself how to be patient in his down time in Korean hotel rooms. Let’s even look at players similar to Mondesi’s age-22 season from a swinging perspective and if they got better:

On average, those players roughly shaved off ~1-1.5% on average from three categories but also swing ~2% more outside pitches. Some players made large improvements (like Freddie Freeman) and others took steps back (like Adam Jones). Now these 13 players are in now way representative of what will happen, and remember that plate approach and contact go hand in hand. It’s all part of an overall package to get a feel for how a player approaches each pitch. Let’s create a full picture of similar plate approaches to Mondesi’s age-22 season, using both discipline and contact, and see how they aged:

If you think that’s a doozy to look at, it was even more work to put together, but it gives us some information. Z-swing%, Swing%, and Swinging Strike% all stayed roughly the same, while this collection of batters increased their O-Swing%. That doesn’t tell us much.

What is insight though is that there seems to be non-marginal improvements in O-contact% and a little bump up in Contact% overall. This list of similar players is...underwhelming, but there is some evidence that Mondesi could improve his plate discipline as a whole.

Swinging strike rate is one of the key indicators I look at for prospects and MLB players as a proxy for adjusting strikeout rates in my head going forward. In that vein, Mondesi has one of the worst in baseball, similar to another former top prospect Byron Buxton. As Alex Chamberlain of FanGraphs points out, Buxton and Mondesi share similar traits

For their respective careers, both have been plus runners/defenders with power, but their plate discipline numbers have are problematic. Buxton tore apart the league in the 2nd half of 2017 just as Mondesi did in the second half of 2018. Buxton did not carry over his 2017 second half to 2018 (eventually being sidelined by an injury before returning and having his service time manipulated at the end of the year). Those similar issue could be what halts Mondesi next year unless there is improvement.

Batted balls

Going back to xStats and Statcast, Mondesi posted fairly pedestrian numbers in some batted ball data (refer back to the glossary):

xOBA+: 101.1 (1% above average)

OUTs: -0.006 (0.00 is average)

Actual Triple Slash: .276/.306/.498

Expected Triple Slash: .267/.294/.483

Average exit velocity: 87.4 MPH (234 out of 390)

Average batted ball distance: 178 feet (140 out of 390)

Barrel + Hard Contact%: 17.2% (82nd out of 259)

Mondesi also ran an incredible 19.7% HR/FB%, meaning almost 20% of the time he hit a fly ball it left the park. It was even greater in the month of September where it reached 30%.

The bear case is about as simple as the bull case when you boil it down: Mondesi’s peripherals leave a lot to be desired, and combined with a little luck (30% HR/FB% & .341 BABIP), you could see regression coming for him instead of improvement.

I think Mondesi ends up being a ~2ish win player (which is great) rather than a 5-6 win player unless there are improvements in his underlying numbers.

Still, he’s going to be exciting. Someone you hold your breath for every time he puts the ball in play and cover your face when it’s a two strike count. A danger on base and in the field, and sometimes a danger to himself.