Among the many questions facing the Pirates this upcoming season, there are few more pressing than whether Gerrit Cole can stay healthy and recapture his past dominance.

It isn’t that Cole’s performance in 2016 was a disaster. In fact, his numbers would have translated to over 4 fWAR had he pitched 190-200 innings. But his ERA falling out of the upper echelon of pitchers and his strikeout rates resembling those of Wade Miley exacerbated an already volatile and disappointing Pirates rotation.

Let’s examine a few aspects that changed from 2015 to 2016 in Cole’s pitch profile in hopes of identifying what needs to be rectified this upcoming season if he is to build upon his past success.

Cole’s fastball

While Cole wasn’t in the Bartolo Colon 90-percent usage category, few pitchers throw the heater more often than Cole did, as he utilized the fastball (including the sinker) about two-thirds of the time in both 2015 and 2016. Remarkably, the fastball earned a pitch value over 24.2 runs in 2015 (via Linear Weights), trailing only Clayton Kershaw. Unfortunately, it somehow ended up around league average in 2016 thanks to a 283/.348/.406 slash line against it. So what happened?

Velocity

It wouldn’t have been surprising to see a problem with Cole’s velocity in 2016 given the elbow soreness and triceps issues, but Cole still threw just as hard on average as he did the previous season. Even so, he didn’t seem to possess the same range with his fastball from 2015 to 2016. During the 2015 season, his fastball typically saw 8.5-10 mph of range each month, but in 2016, the range sat around 7.5 mph all but one month of the season. If a pitcher is going to be throwing the same pitch with great frequency, it’s paramount that he is able to effectively alter its speed and location to give hitters different looks.

Movement

In addition to contracted range, Cole struggled to replicate the movement he’s displayed in past years. Most of his career has comprised of keeping the fastball vertical movement down with the occasional spike in vertical movement to stun hitters, but his fastball had consistently more vertical movement this year.

As can easily be seen, the four-seamer typically jumped to 8-9 inches on vertical movement, while the sinker was all over the place rather than the paragon of consistency that severely limited hitters in 2015. (The variance wouldn’t be as ineffective on the sinker if the range at a given time was large, but those remained small from month to month.)

Cole’s fastball also has typically run in hard on right-handed hitters at a level only matched by a handful of pitchers, and while it was still above average in 2016, it wasn’t as sharp as 2015.

It may seem a bit nit-picky given how close the values seem on the graph, but the inch at times can make a difference. After all, if Cole is accustomed to a pitch moving in one place, and it’s off by an inch or two, it can be the difference between hanging the pitch over the zone or allowing a hitter to time it slightly easier, versus getting them to whiff or ground out.

In the end, Cole could still be successful with 2016 type of movement, but it is notably different than that of the incredibly successful fastball from 2015.

Location

Overall zone numbers inevitably change to some degree year to year, but since there was increased zone contact and fewer whiffs, it’s worthwhile to see how Cole worked the zone.

The difference from 2015 to 2016 isn’t noteworthy on its own, since Cole faced a variety of hitters. Nevertheless, he did seem to have abnormally high percent in the upper left corner of the zone and just outside of it. There are some scatter profiles that will paint exactly where those pitches landed in a particular zone, but with high volumes of pitches, it’s hard to interpret a great deal from the image. The zone profile does allows us to also look at zone usage with its corresponding swing rates and results to determine if the changes or location were less effective regardless of velocity, movement or sequence.

The seismic shift in whiffs per swing in the zone is disconcerting, especially considering opponents only whiffed twice in the bottom third of the zone (that is, the bottom three of the middle nine tiles). For whatever reason, Cole wasn’t able to blaze past them or deceive them in his usage of the fastball.

In terms of slugging percentage, he was more successful at limiting the damage in the heart of the zone, but he was walloped both low in the zone and in the upper left part of the zone (inside on right-handers). There’s bound to be contact in the zone, but this essentially underlines the notion that the fastball was generally more predictable and easier to hit in 2016.

Cole’s slider

Between 2015 and 2016, opposing hitters went from straddling the Mendoza line against Cole’s slider with a 41 percent strikeout rate to batting .275 against it with a 31 percent strikeout rate while producing 40 percent more runs. With an ineffective primary offering, it is logical that Cole’s slider wouldn’t be effective either since they play off one another. Well, it wasn’t an effective pitch, as it went from a plus pitch to below average in 2016.

Velocity

At 87-mph on average in 2015, Cole threw a reasonably hard slider but still maintained solid separation from his fastball. That velocity started increasing in August 2015, so it’s not entirely concerning to see the 2016 average at 87.6 mph. There is no reason Cole’s slider couldn’t be potent at that velocity, but it does lessen the gap between the fastball, and the data indicates some correlation between his velocity increasing and opponents batting average increasing.

Movement

The hard slider featured strong movement to elite movement both horizontally and vertically, registering top 16 among starting pitchers. Regardless, there is a concerning trend developing the past couple of seasons:

The results came down slightly after the first couple of seasons but remained dominant. However, the change in horizontal movement means the pitch no longer breaks as far away as it used to from right-handed hitters or as far in on southpaws. Additionally, it isn’t breaking downwards with the same authority, which is not surprising given the injuries Cole faced in 2016.

It is difficult to know to what degree the movement was the result of injury or losing feel for pitch, and if it weren’t for following information, it would be easy to blame it all on the former.

The month-by-month numbers suggest Cole was incredibly crisp for a few months in 2014 and the first few months of 2015 before putting up this type vertical movement even before he was injured in 2016. Perhaps the heavy workload had begun to sap his ability to get movement late in 2015. It’ll be quite telling this season if the dominant movement doesn’t return.

Plate Discipline

Cole hit the zone more in 2015, but there was something about the movement and sequencing of the pitch that baffled hitters. When it was outside of the zone, they chased it half the time it was thrown and made contact just 39% of the time in addition to whiffing over a fifth of the time regardless of location.

In contrast, 2016 saw hitters eager to swing in the zone (68 percent) and hesitant to chase it at just 34 percent, suggesting opposing hitters weren’t guessing whether it would be a strike as often — they simply knew. Even when they chased it, they made strong contact rates while whiffing less in and out of the zone.

Here is how drastic the difference in contact made was from 2015 to 2016:

The moral of the story was more than just, “Don’t hang the slider over the plate,” because opposing batters pounded the ones that just missed the lower part of the zone since they weren’t breaking as hard downward on righthanders. And against southpaws, the slider had a tendency to hang low and inside the zone for an easy target. Obviously, this wasn’t the recipe for success.

Final thoughts

There’s more to Cole’s repertoire than just the fastball/slider combo. Granted, he hardly uses the changeup, although, it is worth mentioning that Mike Lavalliere thinks it’s the best among Pirates pitches even if it hasn’t translated to good career results. On a more interesting note, Cole’s curveball was fantastic last season, so he could utilize it more this season, especially if the movement on the slider was attributed to more than injuries.

Nonetheless, Cole needs to prove the movement issues were indeed more than the product of injury than feel if he wants to return to the dominance he once displayed. It sounds easy enough if it’s merely a health issue, but if the slider doesn’t return for whatever reason, Cole needs to have his fastball on point and hone the rest of his arsenal, or he’ll be good or maybe even very good rather than great. That may not seem like too much of a problem, but the Pirates could use stability and excellence from Cole with all the youth and question marks slotted behind him.