Baseball America ranked Taijuan Walker as one of Seattle's top five prospects each season from 2010 to 2013, including as their number one farmhand in 2011 and 2013. In 2015, Walker's four-seam fastball averaged 94.8 MPH, and he unquestionably possesses the velocity to strike out a boatload of batters, but he has struggled with his command. He walked 18 batters in his 38 innings in 2014 while relying on 59 percent fastballs, 15 percent curveballs, and 17 percent splitters.
Walker started 2015 in a similar, inconsistent fashion. April and May saw Walker serve up 23 walks in only 51 innings, but beginning in June he walked only 17 batters in his remaining 118.2 innings. The most obvious change made during this time was a heavier reliance on his top-notch fastball. From the onset, Walker threw fewer curveballs in favor of secondary offerings, including a cutter and the splitter. However, as the season endured, Walker relied more on his fastball in lieu of the secondary pitches. This served him well in harnessing his control, and his walk rate improved dramatically.
Unfortunately, an adverse effect of this change was a seemingly unexpected increase in his home run rate, which increased from 0.47 homers per nine in 2014 to 1.33 in 2015. Walker did not show a propensity to give up many home runs in the minor leagues. For a player who allowed only 27 home runs in 405 innings from his Rookie-ball days until his promotion to Triple-A, the spike is surprising. In 2015, he pitched in fewer than 170 innings but still managed to give up 25 home runs, the 13th-most in baseball.
The root cause in the spike is that despite his improved control, Walker did not command his fastball in the strike zone and left far too many fastballs over the heart of the plate. Per Brooks Baseball, he left a significant portion of his four seamer offerings in the middle of the strike zone which were pounded by opposing hitters:
While it's undoubtedly true Walker induced a large number of whiffs with high heat, the pitches left in the middle or lower part of the zone were often crushed, contributing to a high homer rate:
The inconsistency in Walker's game can be chalked up to him still feeling his way through his repertoire early on in his career and making an adjustment to limit his walks. An unintended consequence was leaving more fastballs over the middle of the plate, which contributed to a massive amount of home runs.
Walker seems to have found the right mix of pitches to harness his control, but in order to make that leap forward he will also have to improve his command. He is the same age as Noah Syndergaard and has plenty of time to develop as a key cog behind Felix Hernandez, but without commanding the zone better he'll never ascend to an elite level.
Steven Martano is an Editor at Beyond the Box Score, a Prospect Writer for the Colorado Rockies at Purple Row, and a Contributor to The Hardball Times. You can follow him on Twitter at @SMartano. Special thanks to BtBS Editor Spencer Bingol, who contributed fantastic insights for this piece and without whom this article would have been far less interesting.