Reviewing the Rotation, part II: Aaron Sanchez

To put it mildly, 2015 has been a bit of a roller coaster for Aaron Sanchez. Not just game to game, but inning to inning. He's had a lot of brilliant innings, generating weak contact on a few pitches, almost Halladay-esque in their blink-and-you-missed-it nature. But equally, there's been a lot of very difficult innings where he loses the strike zone entirely or where his command is poor and he's been hit hard. Below is a high level comparison of 2014 compared to 2015, with the caveat that comparing relieving to starting is apples to oranges (data from FanGraphs):

There's some eyepopping stats here, which is bound to be the case with a pitcher who has given up just 32 hits in 38 innings, but 29 walks and only 25 strikeouts (starting the 8th inning of his May 8th start, he had 24 of each). At a very high level, Sanchez has shown the ability to outperform his peripherals in both seasons, with his ERA over a run below his FIP both years. That's been driven by suppressing hits on balls in play, though to a far less degree in 2015 than 2014. More on that below.

Of course, that performance is worse by about 3 runs per game in 2015. The reason for that is pretty obvious, as his strikeout rate has cratered from slightly above average to well below average while his walks have ballooned from around league average to over double league average. In fact, in the last 40 years there have been 6,472 starting pitcher seasons of at least 50 innings. Only 15 pitchers had a walk rate greater than Sanchez, which puts him at the 99.75th percentile, or three standard deviations below average. This is literally 20 control. Granted, the guy directly above him is Randy Johnson in 1991, and I think he turned out alright (though he also struck out 26% of batters, double Sanchez when adjusting for the increase in strikeouts since).

On the positive side, at 58%, Sanchez's ground ball rate has held up about as well as could be expected given the change in role and natural regression from a very high 2015 number in a small sample. He has however been bitten by the long ball, going from having a below average rate of fly balls leaving the yard to an above average rate. This should tend towards league average of 10-11%, and is mitigated by him giving up so few fly balls in any event.

Turning to his raw stuff, as a starter Sanchez has unsurprisingly dialed back his fastball usage from 88% to 73%, increasing usage of his curveball (11% to 15%) and change-up (1% to 8%) and mixing in that slider/cutter about 4% of the time. That sharp reduction in fastball usage still leaves him 5th in MLB among SP with 20 or more innings, so he's very dependent on it. His velocity is down about 3 MPH from averaging over 97 MPH to between 94-95 MPH, which follows from having to throw 100 pitches an outing rather than 20-30. This is actually a tick or so better than I expected given where he was in 2014 minor league starts, and remains elite velocity.

Just about two months ago, I wrote an article outlining some reasons I was cautious about Aaron Sanchez in 2015. I think it's fair to say a fair bit of those concerns have come to pass. Below, I'm going to analyze his 2015 season through the lens of those concerns, and then add some historical context.

Batted Ball Results

Last year, Sanchez dominated when he allowed contact, both in terms of preventing hits and suppressing power even when controlling for batted ball tendency. This was mostly why he outperformed his peripherals, and I identified this as something which was likely to go backwards. Let's add in 2015:

As a reminder, this is for all non-bunted balls in play, including home runs. On ground balls, Sanchez continues to dominate, though a little less than last year. He's only holding batting average 80 points below average instead of 110; quelle horreur. I'm still inclined to think there's regression coming, but as the sample continues to build, there's more reason to believe this represents a real skill.

Balls in the air are a different story. On line drives, Sanchez was a little better than league average in 2014, but this year he has allowed significantly more power than last year. The only fly ball hit he allowed last year was a home run; in 2015 Sanchez is still preventing some hits, but allowing power more in line with league average.

Consequently, whereas Sanchez was about 150 points of BA and 280 points of SLG better than league average last year, this year he's only better by about 45 points on both counts. He's still managing contact fine, but this makes a huge difference especially with his peripherals going backwards. And looking forwards, I expect continued results in line with 2015 so far compared to 2015.

Strikeouts Looking and Contact Rate

Another potential issue was that in 2014 Sanchez got almost half of his strikeouts looking, whereas overall pitchers get about one-quarter of their strikeouts looking. Of his 8% decline in strikeout rate from 2014 to 2015,  5% is due to a reduction in strikeouts looking (from 11% to 6%). This is more in line with league average, so once again, I think this is more representative going forward.

The swinging strikeouts are down too (by 3%), but his contact rate is actually a bit better overall. They're down mostly because Sanchez is not doing a good job getting into strikeout counts (23% of pitches thrown with two strikes vs. 28% league average), and his contact rate is a little higher with two strikes. That should probably even out a little, so his swinging strikeout rate might tick up a little bit.

Strikethrowing Ability

This is the elephant in the room, as in 2014 Sanchez was consistently falling behind, mostly because of a poor ratio of balls to called strikes. Unfortunately in 2015, contrary to offseason claims of improvement, things are even worse.

To start with, in 2014 batters were already taking a lot of pitches, 57% of Sanchez pitches vs. 54% league average. In 2015, they're now taking 62%. And why not, because most of them are balls: Sanchez's ball rate of 43% is 7% above league average, while his called strike rate is only about 1.5% higher. That's a great tradeoff for a hitter, and a big reason the walk rate is so high.

The bottom line: MLB pitchers throw about 22% of their pitches in what I consider hitter counts, and about 37% in pitcher counts. For Sanchez, that's been 31% and 30% respectively in 2015. That's why his strikeouts are low and walks really high, and frankly it's a miracle he hasn't been hit harder given that disparity.

Historical Precedent

I discussed above how Sanchez's walk rate was historically off the charts. But can he be reasonably effective anyway? I looked at pitchers from the list above with a walk rate above 15%, a total of 50 pitcher seasons in the last 40 years. As a group, they averaged 99 innings, with 18.4% strikeout rate, 16.4% walk rate, and .278 BABIP (well below average, especially for a group). However, their ERA was on average 19% above league average, which is pretty awful.

There's pitchers with decent seasons on the list -- Randy Johnson shows up in 1991 and 1992, Nolan Ryan in 1977 for instance -- but they had very high strikeout rates because they missed a lot of bats offsetting their walks. Sanchez has not done this so far. But there's another familiar name to Blue Jays fans: Kyle Drabek.

In 2011, Drabek started the year in the rotation and struck out 14.3% of batters while walking 15.5%. For a while in the early going, he was generating a lot of ground balls and had a low BABIP, and made it work. But when that reverted, things unravelled and he was sent down. And I fear that's the end game here. Though as I see it, there is one major difference, which is that when things went poorly, Drabek would completely lose his composure. Sanchez on the other hand, has kept it together and stayed poised. Maybe that's the X factor that allows him to keep walking the tightrope in the immediate term, while figuring things out longer term.

And One Last Thing

One last thing I noticed is that Sanchez has put up significant platoon splits, both in 2014 and 2015.

Perhaps that's to be expected given his reliance on fastballs, but his curveball should help beutralize opposite handed hitters. He's doing fine against righties with decent peripherals, but getting crushed by lefties. This would seem to indicate he really needs a third pitch (among other things).