Pittsburgh Pirates ace Gerrit Cole has relied on his slider for most of the year, at a level of success that can be downright electrifying at times.

As Bob Dylan would say “The times they are a changing.” But, before we tell you how. Let’s look at Cole’s recent performance.

As the season progresses, we have seen some unfortunate recent outings from Cole, including his most recent poor showing in a 4 inning effort against the Milwaukee Brewers. He was tagged for five runs that day en route to an eventual 7-4 Pirates loss. Cole’s bounce back ability was fully on display in his next outing, a two-hit gem vs the St. Louis Cardinals. After a skipped start, Cole looked rejuvenated against the Cubs before giving in and allowing one rough inning to leave him with a no-decision.

To be sure, Cole gives the Pirates a chance to win more often than not. While he has clearly fallen off of his early season pace, he remains entrenches as the Pirates’ most effective starter. In July, he lasted at least seven innings in each of his starts. Four of his six outings in August lasted at least six innings. All of this should be taken with a heavy asterisk, as many starting pitchers around the league would take Cole’s recent numbers in a heartbeat. This perceived drop in performance is strictly measured against Cole’s own lofty standards. With a 2.60 ERA and a 4.35 K:BB ratio, Cole still stands among the National League elite.

Clearly, there had to be some factor, some morsel of truth that we have all overlooked that could explain Cole’s up-and-down starts (again by his standards) as of late.

At the risk of having you click away from this post, I did not find any. But, I did find something.

I discovered a new-found reliance on a heretofore forgotten pitch.

Cole rediscovered his curveball.

First, a primer – even the experts have issues identifying Cole’s breaking pitches. As pointed out earlier this year in a great piece on FanRagSports, it was noted that the popular pitch tracking tools – notably FanGraphs and Brooks Baseball – have trouble distinguishing between Cole’s slider and curve due to their similar breaking action. Our friend Pat Lackey at WHYGAVS also noticed this back in 2014. For the purposes of my study here, I’ll be using Brooks Baseball’s pitch f/x tools.

As we unpack his newly re-discovered curveball, let’s look at Cole’s 2014 usage against what we’ve seen overall in this campaign. Last season, Cole threw the curveball 321 times over 22 starts, or 14.59 per start. Only six times did he throw the curve less than 10 times in any particular start.

In 2015, that per-start number shrinks in half to 7.41 per start over 29 outings to-date. This drop in usage is directly attributed to his first 15 games, in which it was never thrown more than nine times per start for an average of 4.4 curves per game. In two of those 15 starts, the curveball was not used.

Since those first 15 starts, the curve is seen an average of 10.64 times per game. Why the sudden change in usage? I believe that only Clint Hurdle, Ray Searage, Francisco Cervelli, Chris Stewart, and Cole himself may truly know. In today’s baseball, pitching is fluid. Match-ups and game scenarios heavily dictate usage of a certain pitch over another. Perhaps most influential in Cole’s pitch selection would be the degree to which the pitches themselves are working on any particular night. Hear it from the man himself in a recent P-G Pirates Blog from Bill Brink, after his win over the Cardinals:

[On the curveball]“I just was staying aggressive with it,” he said. “Didn’t get the slider working much. Threw a couple good ones in some situations, but the curveball was playing better tonight for whatever reason. Credit to Cervy for figuring out what stuff was working.”

With the myriad factors determining pitch selection, we should caution ourselves not to make too much of the usage numbers. This is especially true for secondary – or in this case tertiary – pitches. Cole’s bread-and-butter remains the fastball/slider combination.

We can measure results, however. In looking at the curveball usage and its overall effectiveness, several items almost leap off of the page. In 2015, Cole’s curve has always shown to have a good whiff percentage rate despite its early lack of use. Whiff percentage is exactly what it sounds like – percentage of times a batter offers at a pitch and misses. Here’s a look at Cole’s curve use side by side with his whiff rate.

[table id=17 /]

Note: The curveball was tracked as being used only eight times in April.

Most eyes will immediately go to those September numbers, and understandably so. Yet we must practice caution as the higher whiff percentage is almost a direct result of the huge increase in usage. Despite this, all months save for August saw a whiff rate right near or slightly above the current MLB average of 11.11%.

Since August 17th, Cole has thrown at least 10 curveballs per game. The effectiveness of this rediscovery is very hard to quantify. Consider this: In 2015 overall, opposing hitters are enjoying a .316 batting average against the curve. How much stock should we put into this? In my opinion, not so much. Hitters are staying back more often than not on the curve, as it has the lowest swing percentage of all of Cole’s pitches at 37.67% on the year. Selection by a hitter breeds a very binary outcome. Either the pitch is taken or it is swung at. It’s not unreasonable to assume that if hitters are selective against this pitch, then they will offer at instances they feel best about. Thus, a more assured swing can result in a hit.

We can measure results, however. In looking at the curveball usage and its overall effectiveness, several items almost leap off of the page. In 2015, Cole’s curve has always shown to have a good whiff percentage rate despite its early lack of use

A better picture of the pitch comes into focus when we consider opponent’s slugging percentage against his pitch. At a manageable .395 on the year, we find that hitters only managed three doubles against the pitch all year with exactly zero home runs. This, coupled with the whiff rates shown above, paint the picture of a pitch that is hard to track as it approaches the plate, suggesting that batters struggle to truly drive it if they make contact at all.

There have been rough patches with the curve, as shown by a 1.000 slugging percentage against it in August. A ‘rough patch’ seems to be the most appropriate word to describe those times, as the figure for September drops to a miniscule .083 with a much higher usage rate.

The last word on effectiveness – as it should be for curveballs – comes with a look at the K:BB (strikeout-to-walk) ratio for Cole’s curve. That figure clocks in with a 11:1 rating, proving its overall effectiveness and control.

When analyzing this pitch, the last thing I wanted to look at was usage and outcomes against times through the batting order. Here’s a quick look:

[table id=18 /]

As has been a disturbing trend with some Pittsburgh Pirates pitchers – most notable Jeff Locke – the more times they face the order, the less effective they become. With Cole and his curveball this is absolutely not the case, as his line drive and ground ball rates as well as overall batting against the curve show marked improvement. Curiously, whiff percentage is down the third time through a lineup while other metrics show better figures.

The second time through the order would appear to be a problem for Cole’s curveball yet it also carries the strongest swing-and-miss percentage. One could posit that hitters are somewhat expecting it their second time around while pinch hitters later in the game may be taken back (the data represents just the number slots in the order, not any particular batter). Without a more detailed study, that is pure speculation to be sure.

Overall, I find it very encouraging that Cole is mixing in a wrinkle at this stage in his season. It almost seems like a long con of sorts that Cole is playing on opposing lineups. Last year he threw more curves than sliders. In 2015, he starts off the season virtually abandoning the curve in favor of a devastating slider. When opposing manager and scouts think they have a “book” on the 2015 version of Cole, he revives the curve and – by all measures – has turned it into a highly effective pitch.

Chalk it up to yet another sign of maturity for one of the best young pitchers in the game.