Scouting Chris Flexen

How do you attack one of the best pitchers in the KBO?

If you’re a Mariners fan (or MLB fan) who’s looking to learn more about Chris Flexen after his signing with Seattle, I’d recommend checking out my end-of-season report on him which is far more in-depth than this article. You can find that report here.

The Korean Baseball Organization was the first professional baseball league to get started this year after the disruptions that COVID-19 has caused across the world. As in years past, many former MLB players, either towards the end of their playing days or looking to improve and return to MLB, are playing in the KBO. One of those players, Chris Flexen is in the latter category.

Flexen is a 26-year-old who was drafted back in 2012 out of high school by the New York Mets in the 14th round. Standing at 6’3”, 249 lbs, Flexen poses an intimidating figure on the mound in Korea. Flexen is in the midst of his first season in the KBO, pitching for the Doosan Bears and has been one of the better pitchers in the KBO. As I have been watching and analyzing KBO pitching matchups, I’ve gotten to see Flexen 3 times over the last month and a half, on May 31st against the Lotte Giants, dominating against the SK Wyverns on June 23rd, and against the NC Dinos on June 28th. I have pitch-by-pitch data from all 3 starts and pitch locations from the last two starts.

The purpose of this article is to examine what makes Flexen tick on the mound and how I think hitters should approach a matchup against Chris Flexen based off of my observations from his previous starts.

A breakdown of Chris Flexen season and charted stats

Chris Flexen has had a couple of rough starts recently that ballooned his ERA up to 4.18, but we can tell he’s a better pitcher than his ERA indicates. His FIP of 3.54 profiles much better relative to the rest of the league and is much more representative of how Flexen has pitched thus far. The unlucky patch that he’s going through has been spurred in large part by his BABIP of 0.325, which is one of the worst among qualified amongst KBO pitchers.

Advanced defensive stats are hard to come by for the KBO, but we can approximate. Of Doosan’s 4 qualified pitchers, both Flexen and Young-ha Lee have FIPs that are at least 0.60 points better than their ERA. Hee-kwan Yoo’s FIP and ERA are about even while Raúl Alcántara’s ERA is about 0.42 points better than his FIP, thanks to his much lower BB% rate compared to the others. To me, this indicates that the Doosan defense is about average, likely accounting for some of Flexen’s higher BABIP as well as general poor luck.

Yet, we can’t let him off the hook too easily because he has struggled with walks this season. He’s walked 7.9% of batters faced, ranking 27th in the KBO. A lot of that has to do with only throwing a strike 63% of the time in the games I’ve seen and a first-pitch strike just 54% of the time, which is definitely below average. After he faced Lotte, I speculated that his control issues may be in part spurred by an inconsistent release point thanks to MLB data on his Baseball Savant page. Unfortunately, since there’s no KBO equivalent of the publicly available data that Baseball Savant has, that remains speculation.

Distribution of Chris Flexen’s velocity

Flexen throws 4 different pitches, ranging from the mid-90s on his fastball down to mid-70s on his curveball. His fastball comes in around 92 mph and is his most heavily utilized pitch. His go-to secondary pitch is his slider, coming in around 86 mph. His changeup, averaging 81 mph is primarily a situational pitch against left-handed hitters (LHH) while his curveball, at around 75 mph, serves the same purpose against right-handed hitters (RHH).

Locations of Chris Flexen’s pitches from his 6/28 and 6/23 starts

His approach against LHH and RHH is pretty similar in broad terms. Flexen works away from both lefties and righties while also using the bottom of the zone as a place to locate his off-speed pitches for swings and misses. He has been an effective strikeout guy this season, with a K% of 21.3% that ranks 12th in the KBO and a Whiff % of 29.7% that is better than what a lot of pitchers in the KBO have posted when I’ve charted games.

So, Chris Flexen throws 4 pitches. But, as a hitter, you really want to know WHICH pitch he’s going to throw WHEN.

Breakdown of what pitch Chris Flexen throws in what count

For each count, I’ve pulled the number of each pitch he’s thrown and compiled it into this table, with green filled boxes indicating he’s likely to throw the pitch in question, red indicating that he likely won’t throw the pitch and yellow indicating some uncertainty. We’ll examine his pitch tendencies by LHH vs RHH a little more in-depth soon, but let’s take a look at his overall approach.

An important thing to note here is that Flexen throws his fastball A LOT, throwing it 59% of the time in the 3 games I’ve seen him (He threw it 58% of the time in 2019 with the Mets, while also throwing a sinker, which I have not seen at all). With that in mind, if you can only bet on one pitch coming, bet fastball. His fastball is his go-ahead pitch, the pitch he throws when he needs a strike, as evidenced by its heavy usage in 2–0, 2–1, 3–0, 3–1, and 3–2 counts.

Once you get away from those counts though, things start to get a little more ambiguous. Each one of his secondary pitches has swing and miss capability, while he also shows confidence in his ability to throw his slider for a strike early in the count. His changeup’s usage is the most notable, coming almost exclusively in 2-strike counts and, as we’ll see later, against LHH. His curveball has a similar usage, being used most frequently with 1 or 2 strikes as a chase pitch against RHH.

Keeping in mind WHEN he uses each pitch, let’s move onto examining each pitch in more detail.


Stats against Flexen’s fastball broken down by RHH and LHH

Chris Flexen’s primary pitch is his 4-seam fastball. Over his past few seasons in MLB, he also displayed a sinker, but its usage dropped from 42% in 2017 down to 3% in 2019 and it appears that he’s phased it out of his arsenal in the KBO. He throws his fastball equally to both LHH and RHH, at 58–59% of the time, averaging around 92 mph with the ability to ramp up to 94/95 mph when he wants to. That velocity has always been Flexen’s calling card, averaging 94–95 mph with the Mets as a reliever, and it separates him from other pitchers in the KBO save for one or two other foreign-born players.

Locations of Flexen’s fastball

Flexen likes to locate his fastball away from both LHH and RHH and in the upper-to-mid portion of the zone. Doing so helps maximize the velocity of his four-seamer, especially when he throws it off of his slider or curveball. He does have a tendency to try and work around the edges of the zone with his fastball, which is why it has a Strike % of 62%, which is a tad below where you might like a guy to be with his primary pitch.

That tendency likely has to do with the way his fastball moves; with the Mets, Flexen’s velocity was in the 71st percentile, but his spin rate was in the 23rd percentile, leading to below-average movement. That’s very clearly reflected in his Whiff % of 17% against RHH and what informs his approach. His Whiff % is a lot higher against LHH, but it’s a much smaller sample, but again indicates how his velocity gives him a tool to fall back on even with less movement.

Hitters should be sitting fastball early in the count. Flexen likes to try and get ahead by throwing a fastball in the zone and away, which in the KBO works as hitters tend to be extremely patient and rarely swing on the first pitch. If he gets ahead on the count or a Whiff on his fastball, he’ll return to it if the hitter fouls off his other pitches or he can’t locate something. Almost every time I’ve seen Flexen give up a hit on his fastball, it’s been down the middle half of the plate, which he only attacks early in the at-bat.


Stats for Flexen’s slider broken down by RHH and LHH

I really like Flexen’s slider as his secondary pitch. There’s not much side-to-side action, but it looks very similar to his fastball out of his hand and then breaks pretty sharply before getting to the plate. Coming in at 86 mph, he again shows the ability to ramp it up to 88–89 mph when needed which is a hard pitch to hit.

Locations of Flexen’s sliders

The slider is a pitch he uses more against RHH, throwing it away from them, either in the down and away corner of the zone or down further as a swing and miss pitch. Against LHH, he’s utilized the slider as another strike pitch, evidenced by his 82% Strike % on the slider against LHH. It’s a pretty good Whiff pitch, with a 30% Whiff rate against RHH and 29% against LHH (in just 11 pitches though), and it really helps him set up his other offerings. He uses one of two ways, either as that chase pitch in 0–2 counts or to get a strike early on.

Right-handed hitters should be looking out for the slider as a Whiff pitch when the count is 0–2 or Flexen is ahead. Otherwise, he does like to locate it in the zone for a strike if he’s not throwing his fastball early in the count. He rarely ever throws the slider once there are more than 2 balls, partly due to the vertical drop that can make it a risk to be called a ball.


Stats against Flexen’s curveball broken down by RHH and LHH

Flexen’s curveball is an intriguing pitch that he primarily uses against RHH. Left-handed hitters should not be focused on this pitch and, as such, I will be discussing its qualities for right-handed hitters.

Locations of Chris Flexen’s curveballs

Flexen uses his curveball as a swing-and-miss pitch against RHH. He locates it down in the zone, only getting a strike 43% of the time, but a 36% Whiff rate. He has to locate it down and, in the dirt, because it’s a very distinctive pitch with a huge amount of vertical drop and a big hump. As you can see in the GIF above, he gets a few swings on curveballs at or below the knee, but when he locates in the zone, the hitters barely even flinch.

Chris Flexen has primarily thrown his curveball in 0–1, 1–1, and 1–2 counts for a good reason. To get into those counts, he’s almost always thrown a fastball and/or slider combo to get into that count and his curveball, down in the zone, can come out of that same tunnel. That’s when his curveball becomes really hard to hit. But the distinctiveness of its shape gives hitters an easy signal to decipher if he tries to throw it in the zone; that’s how he gave up an HR once on his curveball, by leaving it up in the zone after its full breaking motion, making it easy to identify.

His curveball is best utilized pounding below the zone as a chase pitch and that’s when hitters need to look out for it. If he induces a whiff on his fastball or slider as he gets ahead in the count, the curveball is very likely to be his put-away pitch with its similar path early in its movement towards the hitter. LHH shouldn’t be worried about facing a curveball from Flexen unless it’s just as a change of pace early in the count.


Stats against Flexen’s changeup for RHH and LHH

Much like his curveball, Flexen’s changeup is a specialized pitch, but against LHH whereas his curveball is a righty-on-righty weapon with a 19% usage against LHH vs just 5% against RHH.

Location of Chris Flexen changeup’s

Flexen’s changeup is a weapon against LHH, averaging about 81 mph, giving him an offering between his slider and curveball. He’s thrown it for a strike 81% of the time, which includes the 6 Whiffs on 12 swings he’s induced from lefties on the pitch. It’s a lefty weapon due in part to the arm side run that he’s able to put on it, drifting away from lefties at the plate. As shown in the GIF above, throwing it down in the zone has been an effective plan of attack for Flexen. He primarily throws the changeup in 2 strike situations which makes sense given its effectiveness as both a swing-and-miss pitch and being able to locate in the zone.

In an 0–2 or 1–2, Flexen has been more likely to throw the changeup down in the zone being ahead in the count with a little bit of a cushion while in 2–2 count, he elevates the pitch into the lower half of the zone.

Putting It All Together

Now that we’ve taken an in-depth look at every pitch that Flexen throws and when he throws it, how should hitters be attacking him?

Overall, Flexen works away from LHH and RHH, while also working down against righties with his slider and curveball. His fastball/slider are his strike pitches while his curveball (RHH) and changeup (LHH) are his put-away pitches.

Early in the count, hitters should be sitting fastball. It’s his most frequent pitch and the pitch that he can confidently locate in the zone. I’d recommend going to the plate planning on attacking a potential first-pitch fastball; however, KBO customs are different and their patience leads to infrequent swings on the first pitch.

After the initial pitch or two, Flexen frequently throws his slider. If he’s down in the count 1–0 or 2–0 and needs to throw a non-fastball, he’ll throw the slider in the zone. If he’s ahead, 0–2, 1–1, he’ll throw it low and try to induce a Whiff.

If he gets to a 2-strike count, that’s when things start to get interesting. For LHH, they should be wary of a changeup, either in the dirt if it’s 0–2/1–2 or in the lower half of the zone when it’s 2–2. Right-handed hitters are looking out for a curveball in 0–2/1–2 counts. The curveball comes out of the same slot as his slider/fastball, making it hard to pick up on when he throws it low in the zone.

If he falls behind in the count, expect a heavy diet of fastballs in the zone. Once he’s down 2–0, he’ll focus on the fastball, rarely throwing anything else except for the occasional slider.

That is how you attack Chris Flexen when he’s pitching against you.

*Stats from,, Baseball Savant, and data I pulled from KBO on ESPN broadcasts*

Sophomore studying Sport Management and Economics at the University of Texas. Writing about Baseball from an analytical and scouting perspective

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