Dissecting Taijuan Walker’s Fastball From 2021

Taijuan Walker‘s first season with the New York Mets was the ultimate Jekyll and Hyde performance. In the first half, he was an All-Star and one of the league’s top pitchers, but after the midsummer classic, everything mostly went downhill.

It’s easy to see how the right-hander put together two very different seasons into one campaign just by looking at his splits. Through his first 90 innings (16 starts), Walker posted a 2.50 ERA, which was the 10th-best mark in baseball. To put that number in perspective, it was better than Max Scherzer, Gerrit Cole, Shane Bieber, and Robbie Ray. But for hurlers with at least 60 innings pitched in the second half, Walker’s 7.13 ERA was the league’s worst mark.

That’s obviously not what anyone was looking for, especially with injuries hitting the rotation and the Mets needing him and Marcus Stroman to step up.

Potential Sources For This Drop in Effectiveness

What was the cause of this extreme dip in production? There are likely many points of view that can be used here. The most obvious one is workload. After tossing 130-plus innings for three straight seasons between 2015 and 2017, Walker threw a total of 67 1/3 frames between 2018 and 2020. So, the mere fact that he stayed healthy enough to start 29 games while accumulating 159 innings pitched is a huge accomplishment, as well as being helpful for his workload moving forward.

However, it’s worth noting that between the first and second half, Walker’s average fastball velocity actually went up from 94.0 mph to 94.5 mph. This fact leads me to what I wanted to discuss today, as well (it’s almost as if I planned it that way).

One of the many split stats from Walker’s season that’ll make just about anyone gasp at first glance is his homers allowed per nine innings. After having that number down at 0.57 in the first half, it shot up to 2.80 down the stretch. And, sure, this was accompanied by a rise in fly-ball rate (36.8% to 46.7%) and hard-hit rate (29.5% to 35.4%), but when we look a little deeper, it was his fastball — his four-seamer, to be more specific — that dealt with a lot of these pains.

Digging Into Walker’s Fastball Metrics

On a per-100-pitch basis in the first half, Walker’s four-seamer had a value of 1.78, which was among the best in baseball, according to FanGraphs. After the All-Star break, that value dropped to -1.70, which was among the worst in baseball. Of the 26 dingers he allowed in 2021, 13 of them were hit off a four-seamer.

When looking at all five of Walker’s pitches (four-seamer, slider, sinker, splitter, curveball), only his four-seamer produced a fly-ball rate above 35.0%, and it was all the way up at 51.1%. The 23.4% ground-ball rate his four-seamer produced was also the only pitch in his arsenal with a rate lower than 40.0% in that category.

This wasn’t a trend throughout the year, though — it progressively happened as the months wore on. Check out how his fly-balls-per-balls-in-play number shot up from July through the end of the year (graph courtesy of Brooks Baseball).

Not surprisingly, this also led to a rather drastic increase in Isolated Power numbers from opposing hitters over the same period of time.

For a pitcher like Walker, who needs to control quality of contact since he’s not a huge strikeout guy (22.3% in ’21, 21.6% for career), this was the opposite of what needed to happen following the midsummer classic.

Moving Forward to 2022

How important is it for Walker to have his four-seamer under control and effective throughout a season? Pitching in the big leagues is obviously more than just using one pitch — for a starter, at least. However, having an effective four-seamer essentially lays the foundation before building the proverbial house when it comes to forming a plan of attack against opposing hitters.

Upon peeking at his pitch usage numbers again, Walker has always used his four-seamer much more than any other pitch in his arsenal. He tossed it 911 times in 2021, with his second-most used pitch being his slider, which he threw 546 times.

This season was huge for Walker in a few different ways. Obviously, being named an All-Star for the first time is something he’ll never forget. The same can be said about those second-half struggles because there were likely plenty of lessons learned as he navigated through those tough times. We ultimately got spoiled by his first-half performance because it was so good and that level of production wasn’t expected from the right-hander.

What should the Mets be expecting from him next season? If he takes the ball just about every fifth day and finishes with an ERA in the 4.00-4.30 range, that’d be a huge win (this is also assuming New York will fill out the rest of its rotation appropriately this winter). That’s pretty much where he landed in 2021, as his ERA was 4.47 in 159 innings, but a little more consistency overall would be lovely.

Getting his four-seamer back on track will be key to this happening in 2022, and getting a full-season workload under his belt for the first time since 2017 will be a huge help in making that happen.