On Taijuan Walker after a tough night

After the Diamondbacks used Zack Greinke and Robbie Ray for three innings each in the NL Wild Card Game on Wednesday, they turned to Taijuan Walker in a pivotal Game One NLDS matchup against Clayton Kershaw and the Dodgers Friday night in Los Angeles. That didn't turn out so well. Walker gave up four runs on four hits before registering an out in the first inning, eventually recovering to strike out 3 batters. After facing the entire batting order in a 48 pitch inning. Arizona lost, 9-5.

Though Walker came up short in a big spot, he has made some big gains this year. The 25-year-old entered his first postseason start coming off a solid opening season with the Diamondbacks (his third full year in the majors)—one that saw him post a 3.49 ERA, an 88.6 DRA-, and 2.5 WAR (by both fWAR and WARP) in 157.1 innings. That relatively low inning total can be explained, at least in part, by missed time: Walker was out for a little over three weeks in May and June with a blister issue, and skipped another start due to the birth of his first child.

There were also performance reasons for the low inning total: Walker’s ineffectiveness the third time through the order (.357 wOBA, .865 OPS, 5.97 ERA), combined with a penchant for generating high pitch counts, led manager Tory Lovullo to remove him in the middle of games almost exclusively—he recorded an out in the seventh inning just four times in his 28 starts, but made it through at least five innings all but twice.

It’s a five-pitch mix for Walker, keying off a four-seam fastball in the 92-96 mph range that he throws a little more than half the time. He complements the fastball with a mid-70s curveball, an 84-88 mph pitch with glove-side break that gets called a slider or a cutter depending on who you’re asking, a splitter (87-90 mph) with arm-side run that ends up looking and working like a change-up, and a seldom-used two-seamer.

Source: Baseball Savant

While his walk and strikeout rates have remained relatively constant, Walker’s improved top line numbers can be traced to a significant increase in his ground ball rate (from 44.1 to 48.9 percent), and a significant decrease in his home run to fly ball ratio (from 17.6 to 11.3 percent), possibly stemming from a strategic adjustment to the location of his fastball.

Pitch Tunnels

As the first .gif below indicates, Walker has made a concerted effort to throw his four-seam fastball closer to the glove-side and higher this year, perhaps to set up his curve and splitter through the use of pitch tunnels.

Source: Baseball Savant

Source: Baseball Savant

Walker’s curveball heatmap has followed a similar progression, with a slight shift upward and a much greater concentration of pitches in the bottom corner on the glove side. Finally, all this coincides with a gradual shift upward of Walker’s vertical release point, as well as a tightening of vertical release point among his pitches.

Source: Brooks Baseball

The idea behind pitch tunnels is to make pitches look as similar as possible up until the “tunnel point”—the point, approximately 23.8 feet in front of the plate, at which a batter needs to make the decision to swing or not—enhancing the effect of pitch movement that occurs after the tunnel point.

Looking at Baseball Prospectus’ total numbers for all of his pitch pairs, Walker rates significantly above average both in break differential and break to tunnel ratio, indicating both that his pitches break significantly after the tunnel point, and that he does a good job of clustering his pitches at the tunnel point in the first place. Walker’s break differential is 3.08 inches compared to an average of 2.6 inches, and his break to tunnel ratio is 29.8 percent compared to an average of 27.6 percent.

Tendencies and Usage Quirks

A few other things worth noting about Walker: he mostly stays away from the slider/cutter against left-handed hitters, throwing it outside to right-handed batters, often as a first pitch or when he is ahead in the count. His curveball usage was way up in September, rating as his most-used secondary pitch in each of his last four starts. The curveball is also his best strikeout pitch, yielding a 13 percent swinging strike rate. He used the pitch slightly more than even his fastball against left-handed hitters in his last start of the season.

The splitter, on the other hand, is a pitch that Walker throws more often for strikes, in an effort to induce soft contact—he has induced a 64 percent ground ball rate on the splitter this season (the highest among all his pitches), while only inducing whiffs eight percent of the time with that pitch.

Walker has a modest reverse split over his career (.735 OPS against RHH, .717 against LHH), and that has carried forward into this year (.736 and .727).

Back to Friday

With Walker’s season-long profile in mind, let’s take a look at the data from Friday night. As you can see from the chart below, Walker struggled to make competitive pitches with his high fastball, and never really got a feel for his curve. That made it easier for batters to lay off his splitter: of the six splitters he threw, five were called balls, and the sixth, a bad belt-high miss, was slapped into center field for a single by Cody Bellinger.

Source: Baseball Savant

Constantly behind in the count, with no one biting on the curve or splitter, and with right handed batters able to foul off the slider, Walker found himself throwing fastballs over the heart of the plate in 3-2 and 2-2 counts to the top of the Dodgers lineup. That is not what you want.

Source: Baseball Savant

Depending on how this series goes, there’s a very real chance Walker could pitch again in relief, perhaps in a more comfortable setting in Phoenix. In fact, his manager said as much:

The adjustments Walker has made this year have yielded real progress, but have not left him impervious to playoff nerves and the erosion of fastball command that comes with them. The Dodgers would do well not to underestimate him if they see him again later this week.

Ross Drath is a contributing writer at Beyond the Box Score. You can follow him on twitter @looselids.