Rick Porcello was really good in 2016 when he won the Cy Young award. He had a very strong 3.40 FIP, an even better 3.15 ERA, and was worth 5.1 WAR. The race was close that year, with Porcello narrowly edging out Justin Verlander. Corey Kluber, Chris Sale, and even Zach Britton all also had decent arguments for the award. Any one of the starters could have won, but Porcello got the nod in what was presumably his career year.

It’s early, but so far Porcello is putting those presumptions to the test. Through four games, Porcello has 23 strikeouts against just one walk with a fantastic 1.74 FIP and 1.40 ERA. He’s never pitched quite this well before.

Even during his 2016 campaign, Porcello never put together a stretch as good as the one of which he’s in the midst. The graph below shows rolling four-game stretches since Porcello came to Boston.

We are currently at the low mark for both ERA and FIP during Porcello’s tenure in Boston. As to why Porcello is on such a great run, we can start with the lack of home runs. Since joining the Red Sox, Porcello has never produced a four-game stretch without allowing a homer until now. He had a couple per year back in his extreme pitch-to-contact ground-balling days in Detroit, where the park suppressed homers, but he had no such streaks during his first three seasons with the Red Sox. Some of that can be chalked up to good fortune, of course: he is obviously going to give up a dinger at some point this season. In addition to keeping the ball in the yard, though, there’s also that 23:1 strikeout-to-walk ratio.

So what’s the difference? Is there even one?

In terms of repertoire, Porcello is roughly the same pitcher he’s always been, emphasizing his two-seamer while throwing a four-seamer, change, slider, and curve, as well. As to how often he’s throwing those pitches, that has evolved a little. He’s throwing his changeup more, and that’s something he wanted to emphasize this season. The table below shows Porcello’s pitch usage from 2015 to -17 compared to the early part of this season.

Rick Porcello Pitch Usage Changes Pitch Type 2015-2017 Usage 2018 Usage Difference Four-Seam 25.9% 14.6% -11.3% Sinker 36.3% 39.9% 3.6% Change 10.1% 15.4% 5.3% Slider 12.9% 23.5% 10.6% Curve 14.4% 6.5% -7.9%

Porcello has emphasized his change, and the difference is even more pronounced when you consider he was the lowest level of his career at 8.3% last season. However, the biggest differences have been made with the four-seamer, slider, and curve. Porcello has reduced the usage of the the four-seamer and curve and increased the usage of the slider. Those changes are significant when it comes to throwing pitches for strikes, inducing ground balls, and getting swings and misses.

First, let’s look at Porcello’s ability to throw pitches for strikes by pitch along with the changes in repertoire.

Rick Porcello Strike Rates by Pitch Pitch Type Usage Change in 2018 Strike % 2015-2017 Four-Seam -11.3% 69.5% Sinker 3.6% 69.4% Change 5.3% 68.8% Slider 10.6% 66.5% Curve -7.9% 54.4%

Porcello throws a lot of strikes, but the one pitch that doesn’t net as many, whether through taken strikes or swings, is the curveball. Usage is down with the curve so that means more strikes for Porcello. Now let’s look at whiff rates.

Rick Porcello Whiff Rates by Pitch Pitch Type Usage Change in 2018 Whiff % 2015-2017 Four-Seam -11.3% 14.5% Sinker 3.6% 4.4% Change 5.3% 13.0% Slider 10.6% 14.2% Curve -7.9% 8.4% SOURCE: Brooks Baseball

He loses whiffs by decreasing the use of the four-seam but gains those back on the slider. Similarly, the sinker and change net out with the curve. So we have Porcello getting more strikes by minimizing the curve without losing anything when it comes to swinging strikes. His strikeouts can stay at a similar level while walking fewer batters, which is what we’ve seen this season. Now, let’s examine the ground-ball rates for each pitch.

Rick Porcello Ground Ball Rates by Pitch Pitch Type Usage Change in 2018 GB Rate 2015-2017 Four-Seam -11.3% 26.7% Sinker 3.6% 49.2% Change 5.3% 40.3% Slider 10.6% 46.6% Curve -7.9% 48.1% SOURCE: Brooks Baseball

The pitch with the lowest ground-ball rate is the four-seamer, and that’s the pitch he’s utilized the least relative to previous seasons. That means more ground balls and fewer home runs. One other aspect where Porcello has changed this year is on the first pitch. Here’s how the pitch usage has changed in the first pitch to a batter.

Rick Porcello On the First Pitch Pitch Type Usage 2015-2017 Usage 2018 Difference Four-Seam 16.7% 1.0% -15.7% Sinker 46.2% 66.0% 19.8% Change 6.5% 5.0% -1.5% Slider 10.0% 17.0% 7.0% Curve 20.3% 11.0% -9.3% SOURCE: Brooks Baseball

Fewer curves and more two-seamers mean more first-pitch strikes, and Porcello’s 69% first-pitch-strike rate is well above his career average of 62%. On first-pitch two-seamers, only 29% are taken for balls. Nearly half are taken for strikes, with the rest divvied up between fouls, a couple whiffs, and ground balls. Not a single first-pitch sinker has been hit in the air off Porcello this season, per Brooks Baseball. It remains to be seen if he is getting too predictable with the pitch and batters will catch on, but it isn’t as though batters shouldn’t already be looking for Porcello’s signature offering. It’s likely he will have to change things up a bit more going forward.

Right now, though, by increasing the slider, change, and sinker while dropping the usage on the four-seam and curve, Porcello accomplishes the following:

Throws more strikes through the decreased use of the curve, particularly on the first pitch to hitters. Maintains his whiff rate by increasing the slider even as the four-seam usage goes down. Increases his ground-ball rate by decreasing four-seam usage.

Thus far, that’s yielded a 23% K rate, the highest of his career, a 1% walk rate, clearly the lowest of his career even if it won’t stay that low, and a 49% ground-ball rate. The ground-ball rate isn’t anywhere near what it was when he pitched with the Tigers, but it would be the highest with the Red Sox. When Porcello was getting those high ground-ball rates with the Tigers, he wasn’t missing many bats. When Porcello was great in 2016, he was missing a decent amount of bats and he wasn’t walking anyone, but his ground-ball rate was lower. This looks like the best version of Porcello we’ve ever seen.