Michael Wacha has evolved post-shoulder injury, but is it for the better?

Early in the 2015 season we here at VEB began to wonder about Michael Wacha. Scooter and I discussed on the podcast Wacha's largely absent changeup, increased cutter usage, low fourseam whiff rate, and uptick in grounders. Some of those trends have continued; others have waned. Joe wondered where the strikeouts had gone at the start of May. They still haven't really shown up. The result so far has been a shiny ERA and a pitching "wins" versus pitching "losses" tally that is downright sparkly. However, Wacha's peripherals were odd. So much so that last week I wrote about whether Wacha's peripherals made his sterling start likely carry through to the finish line of the 162-game marathon.

I want to break down the differences for Wacha pre-shoulder injury and post-shoulder injury in a bit more detail this morning. The following chart shows Wacha's career to date subdivided as follows: 2013 regular season ('13 RS), 2013 postseason ('13 PS), 2014 pre-shoulder injury ('14 BI), 2014 post-shoulder injury ('14 AI), and 2015 ('15). The post-injury 2014 numbers do not include the 1/3 of an inning he threw in the decisive game of the NLCS.

Wacha's Stats: 2013-15

It's fair to say that Wacha's control and command were lacking when he returned to big-league action after months on the DL with a shoulder injury. One of the heartening developments of the 2015 season is Wacha's improved control compared to his post-injury pitching last season. He's walking batters at a career-low rate, which is a positive thing.

As Joe noted a few weeks back, Wacha's strikeouts have dried up. But the lack of Ks didn't begin this April. It can be traced back to his return to game action post-injury. Wacha struck out a lower share of batters during his 16 2/3 innings of work last season post-shoulder injury than this year (an admittedly tiny sample, but one that was apparently enough for the Cardinals to banish him from the postseason and into the Shelby Miller memorial reliever role). Unfortunately, Wacha's K% has not gone up all that much in 2015. It's still well below the big-league rate for starting pitchers after being comfortably above-average in 2013 and his pre-injury days in 2014.

I like to compare apples to apples as much as I can when evaluating a player's stats. Because Fangraphs makes it easy to divide relievers from starters, I try to compare starter averages to starters and reliever averages to relievers. Here are the K% and BB% for MLB starters in 2013, 2014, and 2015 (entering play on Sunday):

• 2013: 18.9 K%, 7.4 BB%
• 2014: 19.4 K%, 7.1 BB%
• 2015: 19.2 K%, 7.2 BB%

Wacha was striking out batters at a rate 13.4% above the average for a major-league starter before injuring his shoulder in 2014. Up to this point in 2015, the righty is notching Ks at a rate 15.6% below the collective rate for big-league starting pitchers. Why? Fewer swings and misses.

Fangraphs swinging-strike rate (SwStr%) measures the percentage share of strikes that are swung at and missed. Wacha induced a swinging strike 11.4% of the time during the 2013 regular season compared to 8.8% for MLB starters overall. (Fangraphs doesn't have postseason SwStr% on the site that I can find). In 2014, Wacha posted a swinging-strike rate pre-injury of 10.7% and 8.1% post-injury. Big-league starting pitchers put up an 8.9 SwStr% last season. This year, Wacha's SwStr% has dipped to 8.5%. The MLB starter swinging-strike rate for 2015 so far is 8.9%. As with his K rate, Wacha has gone from well above average to below average, though his SwStr% suggests his K% should not be as far below average as it is.

This naturally raises the question of why Wacha is inducing fewer empty swings. Thankfully we have the indispensable Brooks Baseball to explore this question. Unfortunately, Fangraphs' SwStr% reflects swings and misses as a percentage share of total pitches while Brooks measures whiffs, which are swings and misses as a percentage share of total swings. Brooks also doesn't have MLB starting pitcher collective whiff rates (that I know of). Nonetheless, whiff rate offers us a metric by which we can compare Wacha in his current form to Wacha pre-injury.

In looking at the Brooks data while attempting to answer this question, it became apparent that Wacha's pitch usage was intertwined with his whiff rate. So I put together a chart that shows Wacha's pre-injury usage and whiff rate for each pitch he throws and the same post-injury. The chart is interactive. If you move your cursor over it, you can see specific numbers.

Prior to Wacha's injury, the righthander could fairly be categorized as a two-pitch pitcher. He threw his fourseamer (4S on the chart) almost 62% of the time and his changeup (CH) about 23% of the time. And why not? Wacha induced a whiff 22.75% of the time with his fourseamer and an astounding 33.46% of the time with his change.

Things have changed since Wacha's injury, though. As Craig first noted at VEB late last season, Wacha began using his change far less often. There was some speculation that this was because of his poor fastball command—Wacha couldn't set the change up effectively with his fourseamer because he could not locate his fastball. However, Wacha's fourseamer command has improved, but his changeup usage has dropped to 13.52% this season. The change's whiff rate has fallen as well, to 25.24%. Still healthy, but not as otherworldly dominant as it once was. Perhaps relatedly, Wacha's fourseamer whiff rate has also fallen, to an uninspiring 16.85%.

Wacha has filled in his lessened reliance on his fourseamer-changeup combination with two pitches. The Aggie is throwing his curve slightly more often (9.18% pre-injury vs. 12.87% post-injury) and experienced increased success with the pitch post-injury (20.69% whiff rate vs. 33.82%). However, this is a small portion compared to the cutter.

Wacha threw his cutter just 5.92% of the time before he injured his shoulder. Since returning from the DL, Wacha has used the pitch 15.03% of the time. The pitch has induced whiffs at a 14.42% rate—far below either his fastball or changeup, even after those pitches' post-injury downturn in effectiveness as measured by whiffs.

Saturday night gave us a taste of what Wacha's ERA bending toward his peripherals will look like. Entering the game, Wacha had posted a 1.87 ERA compared to a 3.63 FIP. The four runs plated by the Dodgers in Wacha's 5 2/3 innings pitched pulled the righty's ERA toward his FIP as his season-high seven Ks to three walks and no homers allows lowered his FIP. It's a wonderful, tiny example of how regression works both ways. Today Wacha's ERA sits at 2.27 and his FIP at 3.76. As the 2015 season plays out, that gap ought to shrink even more.

Another of the reasons we ought to expect Wacha's ERA to go up is his batted-ball profile. MLB starters' BABIP last year was .296. This year it's .295. Wacha has posted a below-average BABIP pre-injury. After returning from the DL it's even lower.

Wacha's Batted-Ball Stats: Pre-Injury vs. Post-Injury

We know that pitchers have an impact on their batted-ball profile. Jake Westbrook is an example of a sinkerballer who set out to induce grounders and was successful in doing so. Wacha is not that type of pitcher, though. He barely throws a sinker at all. Before his injury, he was more a fly-ball pitcher than a grounder inducer. Post-injury, Wacha is generating more grounders, but he's still below the MLB collective GB rate for starters, which was 44.6% in 2014 and is 45.5% so far in 2015.

According to a recent 538 article by Rob Arthur, pitchers account for about 1/6 of the strength of contact batters make against them. Looking at Wacha's batted-ball data using the hardness of contact buckets available on Fangraphs that somewhat resemble Goldielocks's porridge tasting, Wacha's hard-hit batted-ball rate has dropped considerably post-injury and his soft-hit rate has gone up. Wacha post-injury more closely resembles the collective MLB starter rates for quality of contact, which sat at 18.5% soft, 52.3% medium, and 29.2% hard entering play on Monday.

All of this is to say that Wacha's batted-ball and contact-quality profiles are average-ish. In other words, they don't support a BABIP well below average for a starter.

I included SIERA in the batted-ball chart above. It's an ERA predictor that looks backward and takes a pitcher's batted-ball profile into account, which is something that neither FIP nor xFIP do. FIP and xFIP are based solely on strikeouts, walks, hit batsmen, homers, and innings pitched. You can read more about SIERA here. SIERA expects an even harsher upward bend in Wacha's future ERA than FIP or xFIP.

Has Wacha's early-season results been enjoyable to watch. Yes. Do I hope he continues to defy his peripherals and post an absurdly low ERA? Of course, though my hope of all hopes is that Wacha's peripherals improve, he remains healthy, and gives us an elite performance along the lines of Adam Wainwright's 2014 (which feels within the realm possibility, especially with Wacha's cutter usage). Nonetheless, it's fair to say that Wacha has not pitched anywhere near as well as his ERA or his pitching "wins" and "losses" totals suggest. There isn't much reason to believe Wacha to continue to be the elite run suppressor he has been during the season's opening months unless something changes—namely, more strikeouts.

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