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Carter KieBoom or Bust?

Consistent Minor League success led the Nationals’ Carter Kieboom to the top of the team’s prospect rankings. MLB Pipeline ranked Kieboom as high as the 20th overall ranked prospect after the 2019 season. The hype was there, and the Nationals seemed committed to playing Kieboom regularly in 2020. I even picked Carter Kieboom as my National League Rookie of the Year.

Unfortunately, 2020 was a rough season for Kieboom, who exhausted his prospect eligibility. Many question marks surround the 23-year-old third basemen heading into 2021. Will he have a spot? Can he have success at the big league level? Will he be a quad-A player? Let’s look into his profile and see what we can figure out.

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Carter Kieboom, is there still upside?

Prospect Pedigree

Carter Kieboom MILB

I previously mentioned, Carter Kieboom has the prospect pedigree. He was rated as high as 20 on MLB Pipeline and 21 on Fangraphs. Most scouts were impressed by his plus bat speed and balanced swing at the plate. He comfortably hit the ball to all parts of the field as a prospect and exhibited plus raw pull power.

Hit Tool

I graded Carter Kieboom at a 50 hit tool with a future 55 grade. Other sites had his hit tool across the board, ranging from 45 to 60. He often showed his ability to hit in the Minor League. In 1462 MILB plate appearances, Kieboom batted .287. He also displayed good plate discipline and walked at a high clip, leading to a MILB career .378 OBP.


I previously mentioned Kieboom’s plus pull power. Scouts also varied on his future power projection. Some graded the potential power as average, while others believed he had above-average power. Fangraphs actually graded his raw power at 60. Despite the grades, Kieboom hit 45 career home runs in the Minor Leagues with a season-high of 16 in both 2018 and 2019. It will be interesting to see how his power unfolds throughout his career, as he has hit just two career major league home runs in 44 career games.

Rookie Season

Carter Kieboom Stats

Carter Kieboom debuted with the Nationals in 2019, but for just 11 games. It seemed as if after getting the call in 2019 and getting plenty of run in Spring Training, Kieboom was destined for regular playing time in 2020. Despite having five hits in his first four games, it took Kieboom 11 days to play in those four games. His playing time would be consistent for a week and then sporadic until he finally played consistently in September. Unfortunately, Carter Kieboom’s season ended after being struck on the wrist by a 95 mph fastball on September 22.

In Kieboom’s 33 games he played this season, He failed to hit a home run and had just one extra-base hit. He posted a .202 batted average and a putrid .212 slugging percentage. Among hitters with 100 plate appearances in 2020, Kieboom had the worst ISO(Isolated Power) in baseball. Nick Madrigal posted the second-worst ISO at .029, while Kieboom posted a .010. Fortunately, Kieboom posted a high enough walk rate(13.9 percent) to have a respectable OBP at .344. It was far from the ideal rookie season for Kieboom, but what should we expect moving forward?

Plate Discipline

Carter Kieboom Plate Discipline

While it has not been an ideal start to Carter Kieboom’s MLB career, what does his plate discipline suggest? Can he overcome the rough start to his career and get on the right track?

The first number that jumps out to me here is his first-pitch strike percentage. Kieboom saw a strike on nearly 69 percent of his first pitches yet only swung at 32 percent of them. This is a similar problem I saw from Christian Yelich this season. He was too patient, especially on the first pitch.

Overall, I do not think Kieboom was overly patient, though, as his swing rate was only slightly below the league average in 2020. Fortunately, Kieboom chased pitches outside of the zone(O-Swing%) less than the league average. When he did chase, his contact rate was fairly low(O-Contact%) but not terrible.

Kieboom makes up for it when he swings in the zone(Z-Contact%). He posted a 90.9 percent Z-Contact rate, which placed him in the upper tier of hitters in the MLB. So when he swings at good pitches, he makes excellent contact.

Kieboom also posted a low swinging-strike rate of 10.4 percent, which could be a good indication of a lower strikeout rate moving forward. He posted a 27 percent strikeout rate in 2020 but was consistently around 20 in the MILB. His 13.9 percent walk rate was also impressive and was close to his MILB average, which is encouraging giving the other underlying data.

Overall, there are not many concerns in the plate discipline profile. Let’s move forward into his profile and see if there are any other concerning numbers.

Batted Ball Data

Carter Kieboom Batted Ball

Carter Kieboom’s batted ball profile is where things get really interesting. He made positive strides by posting the highest line drive rate of his professional career. Line drives have the highest hit probability of any batted ball type. In 2020, among all hitters, the batting average on line drives was .642. Interestingly enough, Kieboom posted a .722 batting average on line drives. The league-wide batting average in 2020 on groundballs and fly balls was .238 and .166, respectively. Kieboom posted a .053 batting average on fly balls and a .207 batting average on groundballs. The batting average on fly balls was meager, but Kieboom’s BABIP was .299, which is above league average.

Carter Kieboom also posted a healthy spray chart and hit the ball well to all parts of the field. Pulled fly-balls are usually the best way to hit home runs, but hitting the ball to all fields usually leads to a higher batting average. That was not the case for Kieboom. Ultimately, I believe his issue comes down to his lack of hard-hit balls. Let’s discuss that in the next section.

Statcast Profile

Carter Kieboom Statcast

Looking into Carter Kieboom’s statcast data is where I become the most concerned. First, I notice that Kieboom had zero barreled balls in 2020. A barrel is a batted ball event whose comparable hit types in terms of exit velocity and launch angle have led to a minimum .500 batting average and 1.500 slugging percentage. To be barreled, a ball must be struck at least 98 miles-per-hour. Kieboom failed to have one batted ball to become a barrel.

In terms of average exit velocity, Kieboom ranked 323 out of 352 players with an average exit velocity of 85.1 mph. I prefer using average exit velocity on line drives and fly balls, but Kieboom was not any more impressive, with an 89.4 mph average. That placed him 310 of 352 hitters. Okay, not great; let’s see if his max exit velocity was any better? Survey says,.. nope! Kieboom’s max exit velocity was 104.9 mph, rating him once again 323 out of 352. His furthest hit ball of the season only traveled 347 feet, good for second-worst in baseball.

Carter Kieboom’s exit velocity was bad all around, which led to a poor hard-hit rate of 20.9 percent. Only 14 of Kieboom’s batted balls had an exit velocity of 95 mph or higher. Only 12 hitters in the MLB had a lower hard-hit rate than Kieboom.

While his plate discipline and batted ball profile looked fine, the lack of ability to hit the ball hard really hurt Kieboom. It will be an interesting trend to monitor because he showed the ability to hit the ball a little harder in a small sample in 2019.

2021 Outlook

Will Carter Kieboom have an everyday spot in 2021? That remains up for debate. I assumed he would have an everyday job in 2020, but we see how that turned out. Howie Kendrick will be back with the team in 2021, and he played 17 games at third base. Starlin Castro has one season remaining on his contract as well, and he likely has the second base job locked up. Trea Turner is locked in at shortstop, meaning Kieboom may be out of a spot. Kendrick is a more natural fit at DH, but the Nationals could also go out and sign for someone to play third base if they do not feel like Kieboom is ready.

It is hard to say at the moment, but if I had to guess, I think Kieboom’s 2021 ADP settles in around 350 or later. At that price, he may not even be drafted in most leagues. But in deeper leagues with a deeper bench, he could be a nice dart throw. Until we know more about his injury and playing time outlook, I will not invest much into Kieboom for 2021.

Dynasty Outlook

If you own Carter Kieboom in a dynasty league, you have to hold. Do not sell low on him! Now is likely the lowest his value will be in a dynasty league. It could be a good time to check in and see if his owner has soured on him on the flip side. You could be able to acquire him on the cheap and flip a hot 2020 bat like Jared Walsh for him.

Long term, the jury is still out on Carter Kieboom. He has all the tools to be a successful Major League player. It is also important to remember that not every prospect comes up and blows you away. That has become the expectation with young guys like Juan Soto, Ronald Acuña, and Fernando Tatís setting the world on fire right away. Be patient and stay the course with Carter Kieboom. He is only 44 games into his Major League career and has plenty of time to blossom.

Enjoying these deep dives? Be sure to check out David Mendelson’s deep dive on Zack Wheeler and check out what went right and wrong with him in 2020.

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  1. Bill says

    I’ve never understood the basis for Kieboom’s high ranking. Available stats and performance didn’t show much, leaving me wondering what other factors were driiving it — relative age/experience for given level, injuries, projectability, pedigree, etc.

    Articles about individual failed “can’t miss” e are pretty common, but it would be interesting to know what trends would emerge from looking at, say, top-20 prospects that didn’t live up to the hype.

    1. Chris Clegg says

      Yeah, Kieboom never had standout numbers in the MILB. He just always had a great pedigree and the tools that led many to believe he could be a great MLB player. I still think he has the potential to be good across the board, but not stand out in anything particular.

      But yeah, that would be an interesting research piece on prospect busts. Did they have a similar pedigree that is more volatile? Theres a lot of questions that could be discussed. Thanks for the idea.

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