Porcello discovers effective use for heater

For one month early in the 2015 season, Rick Porcello, traditionally a sinkerballer whose fastball sits at 91 mph, led with the four-seam fastball. It was only the second month in Porcello's career in which the sinker's position as his primary pitch was usurped by the four-seamer, and unlike the other instance of this happening, the magnitude of the shift was noticeable.
It was the beginning of Porcello's tenure in Boston, his new home after spending the first six years of his career in Detroit, and so at the time, it seemed like focusing on incorporating the four-seam fastball might've been part of the early organizational roadmap for Porcello. But the experiment didn't go well. In eight four-seam-reliant starts, Porcello allowed 31 earned runs in 48 innings, good for a 5.81 ERA and a 4.76 Fielding Independent Pitching mark. All of his patented ground balls went missing, his homer rate ballooned, he walked more batters than usual and just like that, the four-seam trial run was over. Back to the sinkers he went.
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If it really were an organizational thing -- that the Red Sox encouraged Porcello to use his four-seam fastball more early in the season, if not just to see what it was like -- it doesn't seem like a bad idea, results notwithstanding. Even though Porcello's "heater" only sits at 91, he has the ability to ramp it up to 96, and even more important than that, he's able to naturally generate more spin on his four-seamer than almost any pitcher in baseball. We know that high-spin fastballs can be effective when located up in the zone, because the high spin allows them to defy gravity slightly longer than the hitter may expect, leading to a "rising" effect. That's true even without velocity, and so Porcello seems to possess a real weapon with his high-spin heater.
Gif: Porcello blows one by Teixeira
For whatever reason, though, the plan didn't work, and so it didn't stick. Maybe it was command, maybe it was comfort, maybe it was the way relying on the four-seamer affected the rest of Porcello's sequences, or maybe it was something else entirely. Whatever the case, he went back to the sinker being his primary pitch, and he hasn't looked back since. But the four-seamer is still there. And the way Porcello is using it now is making it more effective than ever. The idea to employ a four-seam approach may not have gone as smoothly as originally planned, but it looks like it's working itself out anyway.
We can start with the basics: through nine starts this season, Porcello has pitched as something like the best version of himself. He's got what would be his lowest adjusted ERA for a season with peripherals that rival his career bests, including a 23 percent strikeout rate that dwarfs anything he posted in Detroit. Porcello is still exceptionally stingy with walks, he still gets ground balls at an average-or-better rate, and now, he can sit a batter down with a punchout when he needs it. Before, there were just too many balls in play -- grounders or not -- for sustained success to seem realistic.
The overall swinging-strike rate isn't up, so what's the cause for Porcello suddenly striking out nearly a quarter of all batters he's faced? This is where we come back to the fastballs. He's actually throwing the four-seamer less than he has in years, as a whole. But it's when Porcello is throwing it, and how he's throwing it, that's changed.
Let's begin with the when. In Detroit, exactly 25 percent of Porcello's two-strike pitches were four-seam fastballs. Since coming to Boston, that rate is up to 36 percent -- he has become more aggressive with the heater when he gets into attack counts. But what's even more striking is how the distribution of four-seamers has changed. As previously mentioned, Porcello is actually throwing the four-seam less than he has in recent years, but that hasn't stopped him from using it as a two-strike weapon:

Throughout Porcello's career, a little less than one-third of his four-seamers have come in two-strike counts. This year, nearly half of his four-seamers are being thrown with a punchout in mind.
And Porcello is getting better at using the four-seam for punchouts, too. He's always been able to generate elite spin on the pitch, giving it that illusion of "rise" that makes it work so well up in the zone. So Porcello has made the obvious choice. The four-seam is going up:

Porcello's head was in the right place last year -- he dedicated more of his two-strike pitches to the four-seamer than ever before -- but the execution was not. The whole point of going to the pitch with two strikes in the first place was to take advantage of its elite spin, but he located far too many of them in the low or middle parts of the zone to do so. Last year, Porcello's average two-strike fastball was 3.07 feet off the ground. This year, that's up to 3.34. Before this season, 73 percent of his two-strike fastballs were above the waist. This year, that's up to 85 percent.
Simply put, Porcello is maximizing the usefulness of the pitch's spin rate by almost exclusively elevating it with two strikes, and it's working. His four-seamer has generated the highest rate of swings of any four-seamer in baseball, and those swings have generated the 12th-highest rate of whiffs per swing. In other words: no one in baseball is getting as many swings -- and misses -- on the four-seamer as Porcello.
What we've got here is a classic case of quality over quantity. When Porcello first arrived in Boston, it looked like the plan was to use more of his intriguing high-spin four-seamer. But when used in excess, that weapon was neutralized. So Porcello went back to his comfort pitch, the sinker, which he's now throwing early in the count more than ever. The sinker is still the primary pitch, and it's still the pitch Porcello uses to get ground balls and ahead in the count. When heightening the quantity of the four-seamer backfired, he heightened the quality instead. More of them dedicated exclusively to two-strike counts, giving his other secondary offerings room to breathe. And in those two-strike counts, more of the heaters are elevated, so as to take full advantage of the spin rate that made it such an appealing weapon in the first place.
It always had the potential. It just took some trial and error by Porcello to figure out how to best deploy it.
A version of this article first appeared at FanGraphs.com.