Figuring out Rich Hill, maybe

It's rare for the baseball world to unite around anything. Generally, nobody's happy to see a great player get injured, and just about everyone is rooting for the pitcher in the eighth inning of a perfect game, but baseball on the whole is a mix of competing interests and desires that rarely align. That makes it all the more special when they do. One of those moments came last year, as the improbable, unpredictable, and wonderful Rich Hill saga unfolded before our collective eyes.

Rich Hill was once a top prospect with the Cubs, and he found some early success with the team, accumulating 4.5 fWAR over only 318 innings from 2005–07. Unfortunately, injuries and control problems saw him demoted to the minors and traded away for pennies. He bounced around from team to team, and in the seven years from 2008–14, he only pitched 153 innings.

He began 2015 on a minor league deal with the Nationals, was released, signed with the independent Long Island Ducks, and finally signed a minor league deal with the Red Sox as roster filler late in a disappointing season. After 32 innings of unexceptional pitching in AAA, Hill was called up on September 8, and something miraculous happened. He made four starts to close out the season, and each one was a gem.

His first game, he struck out 10 batters and walked one in seven innings; his second, he again struck out 10 and walked none. His third game was a complete game shutout, with another ten strikeouts and only three baserunners. His fourth game was disappointing by those standards, "merely" six innings with six strikeouts and three walks. Then, just as suddenly as he was called up, the season ended. Hill was a free agent, and everyone was left to wonder what had just happened, and whether it would carry over into 2016.

Since his emergence, there have been several attempts to explain Hill's breakout, and most have focused on the changes to his curveball and fastball, and the way he utilized them together. In September of last season, only two start into the Rich Hill Experience, Matthew Kory at FanGraphs noted that Hill's curveball featured some of the highest break in the league, and that he used the pitch at an incredibly high rate. As I wrote in May of last season, high usage rates can be a indication of pitches that are better than they look, as the pitch is effective even when the batter expects it. Around the same time, Ryan Morrison at BP Boston examined Hill, identifying the curveballs of Adam Wainwright and Collin McHugh as comparables and noting Hill's tendency to throw his fastball high in the zone. Then, this March, August Fagerstrom at FanGraphs focused on his fastball, and made this amazing chart:

The tentative conclusion from all those findings is that Hill's curveball gained a ton of movement, and by throwing his fastball high in the zone, hitters had trouble distinguishing between the two, making them both even more effective in combination. Not only did this lead to more whiffs (Hill's 2015 contact rate was 75.7%, versus 80.1% pre-2015) and a lot more soft contact (28.6%, up from 18.3%), it came with more pitches in the zone (53.3%, up from 52.7%) and a minuscule walk rate.

I say tentative conclusion, however, because Hill didn't have a single bad start in 2015, making it really difficult to tell what exactly was causing his good starts. For all we know, Hill was like the Giants and even years, except for him, it's years divisible by 13. Or, more plausibly, his transformation had nothing to do with his curveball, his fastball, or his location, but something else entirely that no one identified. I think I can sway with some certainty that I was not the only fan awaiting Hill's 2016 debut with considerable excitement as a result.

That debut came earlier than expected, with Opening Day starter Sonny Gray laid low by the flu. The A's turned to Hill for the first start of the season against the White Sox. For the first time since 2014, Rich Hill was unfortunately something other than outstanding in the Major leagues, lasting only 2.2 innings with 3 strikeouts, 1 walk, and 4 runs. While it wasn't terrible from a fielding-independent perspective, Hill was giving up much more hard contact than he had in 2015 (37.5 percent, versus 28.6 percent last season), and given how important that was to his success, it was certainly concerning. Luckily, his start this past Saturday was a return to his 2015 form: 6.0 innings pitched, 10 strikeouts, 1 walk, and 1 run, with a hard-hit rate of 27.3 percent. Now that we have the ability to compare Hill at his best to Hill while struggling, perhaps we can isolate his magic with more confidence.

The first apparent difference between the two starts was Hill's choice of pitches. Per Brooks Baseball, on Opening Day, he threw 18 curveballs of 66 total pitches, or 27.3%, much lower than his 41.7% from 2015. On Saturday, he looked more like his 2015 self, throwing 54 curveballs of 99 total pitches, or 54.5%. The increased curveball use didn't come at the expense of his fastball, however, which stayed roughly constant at about 40% in both starts; instead, on Monday, he threw 21 sliders (31.8%), versus zero sliders on Saturday.

The slider isn't completely new to Hill, but he's never relied heavily on the pitch. It made sporadic appearances in the early part of his career, was missing entirely in the 12 innings he pitched in 2010–11, and made up about 5% of his repertoire from 2012–15, topping out at 10% in 2013. In 2015, the most he threw it in a single start was during his first, against Tampa Bay on September 15, when he threw it six times (5.5%). The fact that it made up more than 30% of his arsenal on Monday is clearly not an accident.

Hill's pitches also differed drastically in location between the two starts. These charts shows the percentage of pitches thrown to different parts of the zone, with the start against the White Sox on the left and the Mariners on the right:

This is limited just to righthanded batters, to keep inside and outside clear. (Eight of nine White Sox starters were righties, so this is capturing most of his bad start.) On Monday, 33% of Hill's pitches to righties were in the high-and-inside portion of the zone and the adjacent out-of-zone areas; on Saturday, it was only 10%, with most of those pitches shifted to the high-and-outside portion of the zone. Part of this may be an effect of his slider usage – on Monday, most of them were located on the inner half of the plate – but it may also be a cause, in the form of decreased fastball control. Here are the zone profiles for just his fastball, again limited to righties, from Monday and Saturday:

The outside and high portions of the strike zone have exactly 0% of Hill's fastballs in the former, but in the latter, they have 32.5%. While intent is impossible to determine from a zone plot, the latter looks much more like Hill's approach from 2015:

All these conclusions are extremely tentative, based off of two starts, but to me, it looks like Hill had substantially worse fastball control on Monday than he did in 2015, and felt he needed to use his slider much more instead. In the past, he's used his slider very sparingly, and it's been fairly effective: Hill didn't give up a single hit on his 113 sliders from 2012–15, and generated a lot of popups and a similar rate of whiffs as with his curve. However, the slider doesn't have any inherent characteristics (like the curveball's spin and movement) that make it effective: it's slow, averaging around 80MPH, and has little movement either horizontally or vertically:

That means that relying on it heavily probably isn't an option, as it wouldn't seem to be a difficult pitch to figure out. Using it as much as he did against the White Sox means he couldn't throw it for strikes without risking a batter doing some real damage to what is basically a meatball.

It's still far too early to conclusively state that Hill either can or can't replicate his miraculous 2015, but these last two starts show just how important his fastball control is to his success. On Monday, when it looks like he wasn't able to locate his fastball with 2015's pinpoint accuracy, he had to turn to a sub-par third pitch and got hammered as a result. Then,  when he had his fastball control back and didn't throw the slider at all, he looked exactly like the mystifying and effective Rich Hill of last September. Until he develops a third pitch that's effective even when used frequently, it seems the fastball is all that stands between Hill and a return to the abyss.

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Henry Druschel is a Contributing Editor at Beyond the Box Score. You can follow him on Twitter at @henrydruschel.