The Taijuan Walker that shut down the Angels last night is the not the Taijuan Walker that took the mound in April for the Mariners. His early season struggles were well documented, and now his hot streak is garnering just as much attention. I, for one, said that he needed to stay in the majors when he was struggling because his biggest problem was how well hitters were doing when Walker was ahead in the count. He needed to figure out how to put MLB batters away, and I wasn't convinced AAA hitters would provide enough of a challenge for Walker to take this next step.
Here are what Walker's count maps look like now. A reminder that the map on the left shows wOBA by count with red bad and green good. The map on the right shows frequency of counts, with darker shades occurring more often:
Right now Walker is on an incredible walkless tear, with only three this month (!!) However, I could go out on the mound and walk that few batters in a month by simply grooving pitches. Sort of similarly, throwing strikes wasn't really Walker's problem early in the season. His inability to put away batters once he got ahead was his main problem, so part of the reason he walked more batters was because they hung around long enough to draw four balls if they couldn't find a way to square up a pitch before that. Now, Walker is back to destroying batters when they get behind, and his walk rate has predictably plummeted.
However, that is only half the story. Walker has also improved his command slightly but noticeably. 0-1 continues to be his most frequent count, but both 1-0 and 1-1 counts have diminished while 0-2 and 1-2 counts have increased. So, not only is Walker much better in pitcher's counts, he is also forcing batters into more pitcher's counts.
Some of Walker's turnaround is probably some simple regression to the mean. He flashed dominant ability when ahead in the count in his cups of coffee with the Mariners the last few seasons. Now his 2015 numbers look more like that version of Walker too. He will likely have some wild starts between now and the end of the season where he looks more like the April pitcher that had so many worried, but now his overall body of work this season looks more like what was reasonable to expect at the start of the season.
Taijuan Walker has undeniably found his identity again. There's no reason to think he can't keep up the good work as long as he is blessed with his golden fastball, and just as importantly, above average command of it. Walker's secondary stuff, particularly his changeup of late, is good enough to flummox batters once he is ahead in the count, but the high wOBA averages when he gets behind suggests that batters can make Walker very one dimensional when he gets behind. So, his next area of growth is harnessing an offspeed pitch (or two) enough to really start mixing up pitches in all counts. If he can do that, then he'll take another step forward and be a true front-of-the-line starter. However, even if he can't figure that out, he'll be what he is now - a good pitcher that gives his team a chance to win when he's on the mound.