While it’s not at the same level as it was at this time last year, there is still a level of concern around the Red Sox rotation. The addition of David Price certainly helps, but a lot of attention is being paid to the starters behind, and that will continue as Opening Day gets closer. At this moment, Price is getting an expected amount of that attention, and Eduardo Rodriguez is taking another large portion of the spotlight. The attention being paid to the latter has only grown as more news has come out regarding his injury.

One name that has stayed relatively under the radar is Rick Porcello. He was a much bigger story last year after being acquired at the cost of Yoenis Cespedes and subsequently given an $80 million extension. He’ll become more of a focus as the weeks go on considering how big of a season this is for him. He’s no longer burdened with being the proverbial face of the rotation, but the Red Sox still need to see improvement.

No matter which way you slice it, 2015 was a rough year for Porcello. He finished the season with a 4.92 ERA, an 87 ERA+, a 4.13 FIP and a 4.69 DRA. Of course, that doesn’t quite tell the whole story. After returning from a DL stint in August, he looked like an entirely different pitcher. He wasn’t second-half Jake Arrieta or anything, but Porcello finally started to look like the solid starter many were expecting him to be all year.

Most of the time, second-half surges such as this are waved off as small sample size noise, and most of the time that’s the right call. With that being said, this instance seems like something different. There was a tangible change being made in his late-season run.

Earlier in the season, Alex Skillin identified that many of Porcello’s struggles could’ve been due to a change in repertoire. For whatever reason, he started getting away from the sinker that had carried him throughout his career and leaned more on a four-seam fastball. The result was a higher strikeout total, but also a sharp increase in home runs and just hard contact in general. When he returned from the disabled list, he went back to his sinker and the results got better. So, it’s that simple, right?

To figure this out, I got a crucial assist from Jeremy Forsythe. Jeremy pulled individual game logs from all of Porcello’s starts over his career from Brooks Baseball, bringing up both his pitch usage in each game as well as his stat line. From there, he created an Excel file that I could manipulate by pitch usage to give me his results from games that fit my filter. For example, I can get the numbers from each of Porcello’s starts in which he threw his fastball under 30 percent of the time if I am so inclined.

The file spits out his innings, K/9, BB/9, ERA, FIP and xFIP. For reference, here are his career numbers for each of those stats, as well as his numbers from the last three years.

Stat Career 2013-2015 IP 1,245.67 553.67 K/9 5.81 6.83 BB/9 2.17 1.97 ERA 4.39 4.18 FIP 4.04 3.77 xFIP 3.85 3.54

Naturally, the portion of this that I was most interested in was how Porcello pitched with a heavy fastball usage. As previously mentioned, this was a popular theory to explain his poor start to 2015, so I was curious if that had played out over the course of his career. Prior to his injury, Porcello threw his four seamer roughly 31 percent of the time. So, let’s look at his numbers in all of the starts in which he meets that threshold.

Stat Career 2013-2015 IP 158.67 118.67 K/9 5.45 5.99 BB/9 1.59 1.82 ERA 3.80 3.87 FIP 3.98 4.12 xFIP 3.97 3.95

So, that partially goes against conventional wisdom. Porcello is supposed to be worse when he throws a lot of fastballs, but he’s been roughly the same over his career. With that being said, his peripherals have clearly improved if you only look at the last three years.

Now, let’s look at the other pitch in question: the sinker. More fastballs haven’t necessarily killed Porcello like one might think, but maybe we can show that more sinkers means better results. Prior to last season, he threw his sinker 47 percent of the time. Using that as a threshold, his numbers in the starts in which he throws his sinker at least that much are once again surprising.

Stat Career 2013-2015 IP 522.33 116 K/9 5.29 6.52 BB/9 2.58 2.41 ERA 4.76 4.42 FIP 4.36 4.28 xFIP 4.08 3.75

Once again, we’re dealing with a relatively small sample, but this time the numbers are noticeably worse than his career stats. In fact, the numbers get worse as you raise the threshold for sinker usage. This time, that holds for both his career and the last three years Looking at starts in which he threw his sinker at least 60 percent of the time, both his career ERA and FIP stand at 4.67 while his career xFIP rises to 4.20.

The other portion of this to look at is the combination of the two pitches. For this experiment, I tried to pin down the pitch usage he used in his final seven starts of the year to see if he unlocked a key. Specifically, I looked at starts in which he threw between 12 and 23 percent fastballs and between 41 and 60 percent sinkers.

Stat Career 2013-2015 IP 373.67 156 K/9 5.95 7.5 BB/9 2.29 2.19 ERA 4.60 4.10 FIP 4.15 3.69 xFIP 3.80 3.33

This is possibly the most interesting result, as there’s a clear delineation between his career and the last three years. Judging by these numbers, some evolution has taken place over the last few years. Although the career numbers with these restrictions are worse than his overall stat line, he’s been a much better pitcher over the last three seasons with this pitch mix. It’s certainly something to look for this season, as it’s possible that Brian Bannister found something of a sweet spot at the end of last year.

As Jeremy pointed out to me in an email, there’s some evidence that we may be looking in the wrong direction with Porcello. A little over a month ago, Jeff Sullivan broke down some changes the pitcher made with respect to his curveball. It’s not a pitch we usually think of when we talk about Porcello, but it’s been a difference maker. Towards the end of the year, he started consistently throwing that pitch more, and it worked out. Here are his numbers when he throws his curveball at least 10 percent of the time.

Stat Career 2013-2015 IP 556.67 496.33 K/9 6.81 6.84 BB/9 1.99 1.99 ERA 4.27 4.35 FIP 3.83 3.81 xFIP 3.57 3.58

So, a few things stand out here. First of all, that ERA doesn’t really stand out. Of course, we’re also dealing with a sample size that doesn’t even cover a full season, so the peripherals are a better indicator. In these starts, his strikeout rate sky rockets relative to his career, which helps give him a 3.57 xFIP. Now, that’s not my favorite stat in the world, but it works in small sample sizes. The other part of this is that these numbers are relatively close to his overall stat line over the last three years. The reason, of course, is that these numbers make up a large part of his overall stat line. At the very least, these results pique my interest in Porcello’s curveball.

As we look ahead to 2016, much of the hope around last year’s big pitching acquisition will rely on a heavier sinker usage. Although that’s not a bad thing, any hopes that it will completely change his fortunes could be overstated. The same could be said about a lower four seam usage. In the end, the key to all of this could be a newly-utilized curveball. It will certainly be something to watch for as real games get underway, and there’s plenty of room for hope with someone like Brian Bannister in the organization.

Once again, big shoutout to Jeremy for all of his help here.