Chris Flexen, Now With Strikeouts

A former Mets farmhand who amassed 68 innings in the Majors before pitching for a season in KBO (Korea) last season, Chris Flexen 플렉센 signed with the Mariners this past offseason as a real mystery man. Incredibly, he actually entered the 2021 season with more walks allowed than strikeouts during his short MLB career, but a 28% strikeout rate versus just a 6.4% walk rate in Korea suggested that maybe something had changed. So suddenly he was an interesting flyer in fantasy leagues with the possibility he learned something overseas that would translate back to the Majors. That certainly didn’t happen over his first eight starts, but things might be clicking now, as we’ll see over his last five starts.

Let’s now dive into all his metrics, breaking them down into two periods — his first eight starts and his last five.

Over his first eight starts, Flexen was the same low strikeout guy he was before his season in Korea. His SwStk% was poor and didn’t foreshadow any sort of improvement in strikeout rate moving forward. He didn’t sharpen his control, though, as his walk rate fell more in line with his minor league record and solid rate in KBO. But as a fantasy player, the walk rate was far less important since it’s near impossible to deliver any fantasy value with such a low strikeout rate. It’s worth pointing out that his first eight starts included two starts in which he failed to strike out a single batter. It’s not even like he only lasted an inning or two either. He faced 17 batters in his first zero strikeout game and 21 in his second! Those two games sandwiched just a two strikeout game in 27 batters faced. That’s a 3% strikeout rate over three starts! I’ve never seen that before and honestly if that’s the lowest mark over that many batters faced going real far back.

Then something clicked beginning in his May 27 start. While he hasn’t consistently been a decent strikeout guy over all five games during this second period, the aggregate is enough to show a significant improvement. The strikeout rate surge is backed by a big spike in SwStk%. An 11.6% mark is actually just above the league average, which is surprising considering his strikeout rate of 21.1% still remained well below the league average. In addition to the much improved whiff ability, he has also thrown an even higher rate of pitches inside the zone and first pitch strikes. More strikeouts plus fewer walks is quite the combination.

We could all agree that getting tons of swings outside the strike zone is a very good thing, right? It’s hard enough to make contact with such pitches, and even if the batter does, it’s likely to be of lesser quality. That’s a nice surge over his last five games. Not only did he induced more swings outside the zone, batters also found it far more difficult to make contact with those outside pitches. That’s a real sign of the quality of his pitches simply getting much better.

That drop in line drive rate, while a positive, is not sustainable. So while it might be validation of improved performance over a small sample, no starting pitcher can maintain a 14% LD% all season long. Most of those previous line drives have become ground balls. Again, it’s a great tradeoff, but not likely to continue. Surprisingly, his IFFB% is way down, so that somewhat counteracts the lower LD%.

Now it’s finally time to see if Flexen has made any adjustments to his pitch mix or if his velocity changed at all, which might explain all the improved metrics we’ve uncovered. Sure enough, his fastball is up just over a mile per hour over his last five starts. That actually understates the improvement here slightly as the velocity bump actually started in his second start of the second period. Flexen averaged 93.2 MPH with his fastball over the second start of the season, but then hadn’t averaged 93 MPH again through his game on May 27. Then in his June 2 start four games ago, his velocity jumped to 93.3 MPH and it has been above 93 MPH for four straight starts. His last start was the best velocity of the season at 93.9 MPH.

If we look at his MLB career, we find that he’s averaged as high as 96.3 MPH with his fastball, but that occurred as a reliever. So that 93.9 MPH mark in his last start was actually his highest velocity as a starter in the Majors. Both his cutter and curveball also increased in velocity, but interestingly, his changeup barely moved.

His pitch mix hasn’t shifted too much, as he’s thrown his four-seamer a bit more often at the expense of both his changeup and curveball. It’s not a big enough change to believe his expected usage moving forward will be any different given the somewhat small sample sizes we’re using.

While I can’t be sure how much the increased fastball velocity should be credited for his suddenly acceptable strikeout ability, I’d have to think it plays a big role. While there’s no reason to think there’s a whole lot more strikeout rate upside, he’s made himself a streamer candidate in mixed leagues, whereas earlier in the season he was just an AL-Only guy.