It’s been a rocky, inconsistent year for the Seattle Mariners, for whom much was expected by many. They are likely to finish more than a couple games below .500, comfortably out of the very attainable second wild-card position. The stunted development of many of their young, homegrown players, including Mike Zunino and the since departed Dustin Ackley, was a major factor. Early on, it looked like Taijuan Walker, who just recently turned 23, was part of the problem. Around Memorial Day, he began to look like part of the solution. Which version of Walker is the one we can expect to see moving forward?
I was a member of the Mariner front office in 2010, and had extensive involvement in the amateur draft. We did not have a first-round selection that year, but did possess a sandwich-round pick, received as compensation for the loss of Adrian Beltre. As one might expect, our draft board was shot full of holes as our turn approached. We thought very highly of Walker; he was in the top 15 of our board. He was joined there by a couple of other righ-handed pitchers, Aaron Sanchez and Asher Wojciechowski, followed by a bunch of blank spaces where other draft magnets had once resided. The Blue Jays had a bunch of compensation picks that year, and selected both of those guys before our turn arrived.
We were thrilled to select Walker. Great athlete, multi-sport star, easy velocity with feel for his curve ball, very few miles on his arm. As an added bonus, he didn’t turn 18 until August of his draft year. When you’re dealing with a projectable high school athlete, in particular, those few months are actually a pretty big deal. The product of Yucaipa HS in Southern California wasn’t a sure thing, with little track record to speak of, even by high school standards, but the raw materials suggesting potential stardom were certainly in place.
He dominated from the get-go in the minors, breaking camp at full-season Low-A Clinton in his first full pro season. Each year, I compile my own ordered minor-league lists of top full-season-league position-player and starting-pitcher prospects based on performance and age relative to league and level. These basically serve as follow lists, with the orders then tweaked based on traditional scouting methods. Walker ranked in the top 20 in each of his four minor-league seasons, peaking at #7 following the 2013 season. This combination of upside and consistency marked him as a likely major-league star.
As most Mariner prospects from the recent past can tell you, success in the minors is far from a guarantee of similar success at the major-league level. The league adjusts to you, and corresponding adjustments need to be made by the player with the aid of the organization in turn. Walker’s areas of concern as he first ascended to the majors in 2013 centered on the narrowness of his pitch repertoire and his imperfect mechanics.
Walker has never really developed a changeup that qualified as usable at the major-league level. For most starting pitcher prospects, this is a deal-breaker, but when you can dial up easy fastball velocity as Walker does, it’s within the realm of possibility to survive without one. Over time, Walker has added a cutter and splitter to serve as de facto changeups, with mixed results. Even more importantly, Walker’s breaking ball usage has vacillated throughout his pro career. He has experimented with different grips on his curve, and at one point, with the organization’s blessing, even ditched it in favor of a slider.
Mechanically, Walker has had a tendency to finish tall, on a stiff front leg. This has in the past compromised his control and command. His walk rates were a bit on the high side, especially in the low minors, which isn’t unusual for a pitcher so young for his league. The bigger issue, in terms of his major-league future, wasn’t necessarily his walk total, but his ability to command the ball within the zone. Some rough edges needed to be honed for his success to translate to the big time.
As the 2015 season began, Walker was in a pretty rough place with regard to both repertoire and mechanics. Through May 24, Walker was essentially a fastball pitcher. Sure, there were multiple variations, the two- and four-seamer, cutter and splitter, but everything was hard. He had absolutely zero confidence in his fastball, and hitters simply waited for the seemingly inevitable elevated heater — that is, when he was throwing strikes to begin with. It wasn’t easy to watch as Walker compiled a 7.33 ERA through that date, throwing his curve, his only true offspeed pitch, an amazingly low 5.5% of the time.
The M’s could have sent him down, but they endured, and were rewarded, as the light bulb suddenly appeared to go on in his May 29 start. His ERA since then is a much more respectable 3.76, and he has thrown his curve 50% more often, up to 8.4%. Still probably not enough for the long haul, but a meaningful step forward. Perhaps even more importantly, Walker’s mechanics are smoother, and as a result he has been able to command the ball much more precisely within the zone.
To get a more in depth feel for the before and after versions of Walker, let’s look at his plate appearance frequency and production allowed by ball-in-play (BIP) type data for both portions of the season as well as the campaign as a whole. First, the frequency data:
|FREQ – 2015|
The full-season data is on top, followed by his starts through May 24 in the middle, and his starts since May 29 on the bottom. Most compelling are the stark changes in his K and BB rates since May 29. Before then, he had a 19.0% K rate (48 percentile rank) and 11.2% BB rate (99 percentile rank, by far highest in the AL). Since, he’s posted a 23.7% K rate (86 percentile rank) and 3.6% BB rate (4 percentile rank). That’s amazing progress, propelling him into fairly exclusive company. The only two starting pitchers in the majors with K rate percentile ranks over 80 and single digit BB percentile ranks are Max Scherzer and Michael Pineda. When you’re garnering lots of free outs and giving away few free passes, you possess plenty of margin for error with regard to batted-ball authority. More on that later.
As for the BIP frequencies, it’s quite clear that Walker is a fly-ball pitcher. Both before and after May 29, he has consistently run a well above-average fly-ball rate, for a 79 percentile rank for the season. In Safeco Field, this isn’t a bad thing. Most fly-ball pitchers get more than their share of pop ups, and Walker is no exception; he has posted a 69 pop-up percentile rank for the season, with little variation before or after our May 29 cutoff.
He has allowed a high liner rate throughout 2015, at 22.7% for the full year, for a 76 percentile rank, again with little variation before or after May 29. Liner rates fluctuate much more than those of other BIP types, so this is an area ripe for positive regression moving forward. There are a handful of pitchers out there, however, who tend to yield high liner rates on an ongoing basis, and some of them, like Stephen Strasburg and Brandon Morrow, have great stuff, just like Walker.
So we have a pitcher who flipped the K/BB switch at the end of May, and might be in line for some positive liner rate regression. Lots to like so far. Next, let’s fill out the picture, getting a better feel for the authority allowed by Walker by looking at his production allowed by BIP type data:
|PROD – 2015|
|T.Walker||AVG||OBP||SLG||REL PRD||ADJ PRD||ACT ERA||CALC ERA||TRU ERA|
|Thru 5/24||AVG||OBP||SLG||REL PRD||ADJ PRD||ACT ERA||CALC ERA||TRU ERA|
|Since 5/29||AVG||OBP||SLG||REL PRD||ADJ PRD||ACT ERA||CALC ERA||TRU ERA|
The actual production allowed on each BIP type is indicated in the batting average (AVG) and slugging (SLG) columns, and is converted to run values and compared to MLB average in the REL PRD column. That figure is then adjusted for context, such as home park, team defense, luck, etc., in the ADJ PRD column. For the purposes of this exercise, sacrifice hits (SH) and flies (SF) are included as outs and hit by pitchers (HBP) are excluded from the on-base percentage (OBP) calculation.
Before you even begin to dig deep into the numbers, it is pretty apparent that Walker allows harder than league average contact. All of the context-adjusted ADJ PRD numbers, or Adjusted Contact Scores, are over 100, for all BIP types, and before and after May 29. He has allowed .222 AVG-.667 SLG on fly balls for the season, for 156 and 128 seasonal unadjusted/adjusted contact scores, respectively. He has shown progress limiting fly-ball authority, with his Adjusted Contact Score dropping from 151 pre-May 29 to 118 post-May 29. One might think that Safeco Field would have helped him more here, but it was a warm spring and summer in Seattle, and the Safeco effect was quite muted. This offers hope for Walker moving forward. His seasonal line drive Adjusted Contact Score is a harder-than-average 108, with little variation throughout the season.
Walker yielded an unhealthy .421 AVG-.474 SLG on grounders prior to May 29, for a 283 Unadjusted Contact Score that is adjusted way down to 132 for context. He’s been as lucky on grounders since then as he was unlucky before; hitters are batting .198 AVG-.209 SLG on the ground, a 60 Unadjusted Contact Score that is adjusted up to 110 for context. For the year, he has a 116 ground-ball Adjusted Contact Score, with some progress being shown along the way.
Put all the BIP types together, and his 115 and 120 Unadjusted and Adjusted Contact Scores are among the worst in the AL. Even in his hand-picked better portion of his season, he’s still been a below-average contact manager, with a 114 Adjusted Contact Score since May 29. This is borne out by his average velocities allowed, overall and by BIP type. Overall, he’s allowed 90.7 mph average velocity on all BIP, just over two standard deviations above the average of qualifying AL starters, in a tight battle for hardest average contact allowed. His average fly ball (90.6 mph), is over one half, and his average liner (94.8 mph) and grounder (88.5 mph) over one full standard deviation higher than AL average. There has been no meaningful progress made with regard to average BIP velocity allowed throughout the season.
Add back the Ks and BBs, and Walker has been a better pitcher than his 4.70 ERA this season. He’s even better than his 4.18 FIP; his “tru” ERA of 3.91 takes into account the above frequency and authority data. His “tru” ERA prior to May 29 was 5.17, much better than his ERA over that span, but still reflecting his replacement-level performance through that date. Since then, his 3.44 “tru” ERA is again better than his actual mark, and paints him as an above-average AL starter.
Not all that far above AL average, however. Remember, this is a guy with a 111/17 K/BB rate since May 29. You want a little more than a bit above average with that as a starting point. The aforementioned Strasburg and Morrow have repeatedly posted below-league-average Unadjusted and Adjusted Contact Scores, hindering them from approaching their considerable potential. On the other hand, Max Scherzer, a long time below-average contact manager, and Corey Kluber overcame contact management struggles early in their career.
With just league-average contact-management performance, Walker’s post-May 29 “tru” ERA drops to 3.03, which makes him a top-tier AL starter. With just a little better than league-average contact management, say a 90 Adjusted Contact Score, we’re talking legit Cy Young candidate. It’s about way more than just the numbers: Walker must consolidate the improvements he’s made in 2015 with regard to both control and command, while continuing to at least modestly diversify his repertoire. Still, the potential for greatness remains very real for the young hurler who has a real chance to supplant Felix Hernandez as the Mariners’ ace over the next couple of seasons.