The New Ace of the Seattle Mariners?

After being taken in the first supplemental round of the 2010 MLB Draft, Taijuan Walker quickly established himself as a legitimate prospect due to his unique athleticism and his big-time fastball, which led to high strikeout totals in the low minors. He first appeared in Baseball America’s Top 100 list in 2012 at #20 as a 19-year-old, and at #18 in the 2013 list. Jonathan Mayo of MLB.com had Walker ranked as the #4(!?) overall prospect in both 2012 and 2013. But there always seemed to be questions regarding command issues and whether he would fully develop three pitches.

After a few cups of coffee in the Majors, three starts in 2013 and five starts in 2014, Walker broke camp in the starting rotation for the 2015 season. However, things were anything but successful to begin the season. In his first nine starts, the command issues that were a question while he was a prospect were alive in full force. He only made it through six innings in two of those first nine starts, and had 23 walks in 43 innings. He was running an ERA of 7.33 and an FIP of 5.48. Then, on May 29^th 2015, something clicked, as he went eight shutout innings, with two hits, no walks, and eight strikeouts. Ever since, Walker has been a very good starting pitcher, as you can see in the below table comparing before and after May 29^th 2015.

	GS	Innings	K	BB	K-BB%	ERA	FIP
First 9 starts of 2015	9	43	39	23	7.7%	7.33	5.48
Since 5/29/2015	24	151.2	143	20	20.6%	3.26	3.34

Look at that K-BB%! A 20% K-BB% puts him in some pretty elite company. Here’s the complete list of qualified SP that have a K-BB% greater than 20% since the beginning of 2015:

Name	K-BB%
Clayton Kershaw	28.6%
Chris Sale	26.5%
Max Scherzer	25.7%
Carlos Carrasco	23.1%
Corey Kluber	22.5%
Madison Bumgarner	22.3%
Jacob deGrom	22.1%
Chris Archer	21.6%
Jake Arrieta	21.3%
David Price	20.7%
Michael Pineda	20.4%

Not a bad group to be in! Ten guys that we think of as being aces, or near aces, and then Michael Pineda, a solid pitcher in his own right. It’s clear that limiting bases on balls has been key for Walker, and has probably been the main reason why he has improved so much. But why has he gone from walking over four batters per nine innings to around one batter per nine innings? From what I can gather, it looks like Walker tried to focus on two things: getting ahead in the count, and using his off-speed pitches more than he had been doing. In regards to the first point, as Eno Sarris wrote in June of 2015, Walker decreased the usage of his cutter, instead relying more on his fastball, which led to a significant increase in first-strike percentage. Since that start on May 29^th 2015, Walker has a 71% first-strike percentage when he throws his fastball in a 0-0 count, and has been pounding the zone with his fastball no matter what the count is. Information from Brooks Baseball:

Fastball since 5/29/2015
Count	Ball	Strike	Swing	Foul	Whiff	BIP
0-0	32.74%	43.05%	28.48%	13.90%	5.61%	9.19%
Any	29.40%	30.78%	48.79%	21.55%	9.95%	17.55%

Now for the second point, take a look at this article from the Seattle Times in early June 2015. Walker talks about how he was not comfortable with his old curveball, so he changed the grip to a similar one used by Felix Hernandez, and in addition, that he learned to throw a changeup. If we take a look at his pitch mix from before and after that May 29^th start, there is definitely a change in his arsenal. He has increased the usage of his curveball and changeup, suggesting that he has finally gained confidence in his off-speed pitches. Information from Brooks Baseball, but what they are calling a splitter I believe to be his changeup.

Pitch Type	After 5/29/15	Before 5/29/15	Change
Fourseam	60.89%	65.90%	-5.01%
Split	19.10%	16.92%	2.18%
Curve	10.09%	5.51%	4.58%
Cutter	7.62%	11.41%	-3.79%
Sinker	2.31%	0.13%	2.18%

To get to the point of the title of this article, has Walker now become the best pitcher in Seattle’s rotation? The truth is that he has pitched like it since that start on 5/29/15. Using the same stats from earlier, here is how he has performed compared to Felix Hernandez over that time frame:

SINCE MAY 29, 2015
	GS	Innings	K	BB	K-BB%	ERA	FIP
Taijuan Walker	24	151.2	143	20	20.6%	3.26	3.34
Felix Hernandez	25	156	144	58	12.9%	3.98	4.01

Looking at this table, I don’t know if I should be more excited about Walker, or more worried about the King. That being said, you can’t help but be impressed by what Walker has done over his last 24 starts. While the Mariners have the longest playoff drought in all of baseball, and have put together some pretty terrible and/or under-performing teams as of late, a bona fide ace is the one thing that they have had almost since when Felix made his debut in 2005. Walker is not currently a top-15 pitcher, and may never develop into that, but it is clear that at just 23 years old he is becoming a top-of-the-rotation type of pitcher. At a time when it appears that King Felix has entered into a decline phase, the Mariners may have found someone to front their rotation for years to come.