TORONTO — The day after David Price dominated the Rangers back in early July, Christian Vazquez sat at his locker and broke down the pitcher's success in simple terms.

"He was elevating his fastball and changing eye levels," Vazquez said. "That’s the key right now in baseball. Everybody's pitching up. Nobody's expecting that high fastball, so they're swinging."

One of baseball's dominant trends over the last few years has been the evolution of hitters' swing paths and plate approaches. More and more hitters have sold out for home runs and become more adept at hitting for power down in the strike zone; Toronto's Josh Donaldson and Washington's Daniel Murphy have turned improved launch angles on their swings into consistent MVP consideration.

As hitters have evolved, pitchers have had to revise their repertoires. And one major key has been the high fastball.

"Across baseball, there's an obvious shifting mentality," assistant pitching coach Brian Bannister said. "Most teams are willing to make sacrifices here and there. They're willing to play for the home run, and to get that more often, it requires bigger swings that are designed to produce elevation on the ball."

Few teams have made that readjustment as aggressively as the Red Sox. Boston throws the third-most four-seam fastballs in baseball. According to Fangraphs, the Sox get more value out of their fastballs than any other team.

"We talk about it a lot. I feel like we talk about it more than others," pitching coach Carl Willis said. "For years and years, it was always, 'Get the ball down.' The teachings of swing paths now has gotten a little different, and hitters adjust."

"You're just always trying to be one step ahead and have a game plan for what they're trying to do to you," Bannister said. "If they're not aware of something up, then they can just keep that swing that’s tailored toward a low pitch going throughout the entire at-bat. If they never have to feel like they have to cheat with their hands, they get really comfortable.

"With how strong guys are and how well-equipped they are with the data and the launch angles, you're just giving them three chances to hit a home run off you."

Just take one look at the composition of Boston's bullpen. In the past, the Sox had constructed a pen full of strike-throwers who worked down in the zone. Koji Uehara, Junichi Tazawa and Edward Mujica complemented well-located fastballs with splitters that darted under a swing. Burke Badenhop was an old-fashioned relief sinker-baller.

Currently, Red Sox relievers are almost all hard-throwing four-seam guys up in the zone. Craig Kimbrel plays his curveball off his fastball up, much like Drew Pomeranz in the rotation. Joe Kelly switched out his two-seamer for a four-seamer when he made the move to the pen.

"Pitchers have had to readjust their concept of what hitters are trying to do against them," Bannister said.

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Rick Porcello didn't get it at first. In his first few years in the majors, Porcello's concentration was on precisely locating his two-seam sinker down in the strike zone. What need did he have for a four-seam fastball above the zone?

"We'd call it, and it would just be something that I didn't understand the effect it would have on a hitter," Porcello said of a high fastball. "So I didn't have confidence in it, I didn't trust it, and I didn't really use it all that much."

But as Porcello matured, and as he spent more time talking to veteran hitters in both Detroit and Boston, he began to realize the limits of his previous approach — limits exacerbated by the changes hitters were making to their approach around that time.

"That’s the part of the game as a pitcher that you don't necessarily understand at times — what they're seeing in the box and how it impacts even setting up the next pitch. It's kind of learning what can screw those guys up, and then going out and applying it with confidence and being able to throw it effectively and repeatedly."

"You have to get hitters to back off somehow," Bannister said of going up in the zone. "Having multiple weapons and multiple places you can go in the strike zone to get a ground ball or get a swing-and-miss is huge nowadays."

Recognizing the significance of throwing a high fastball was just the first step for Porcello. Being able to actually do it required a whole lot of work — accounting for many of the growing pains he experienced in 2015 with the Red Sox.

"It took time to learn how to throw that pitch," Porcello said, noting that he now feels physically stronger than he did earlier in his career. "An elevated fastball at 88 to 90 is not going to get it done. But at 93, coming off an 88 sinker at the bottom of the zone, that’s a big difference. That’s separation of eye levels and velocities, and it acts as two different pitches."

Porcello excelled in 2016 when those fastballs remained discrete pitches. The high fastball was especially effective for him because of the way it complemented his arsenal.

"A hitter's approach against a sinkerballer is to get him up," he said. "So anything that you throw elevated in the zone, they're going to fire at it. A fastball up, out of the hand, it looks like something they want to fire at. Next thing you know, it's above the barrel.

"It's not rocket science."

Porcello also altered his curveball heading into last season, slowing it down and increasing the vertical break to add depth that would play off a high fastball more effectively. He went from a 4.92 ERA to the Cy Young.

Few pitches work with that high fastball better than a depth curveball.

"It makes their offspeed that much more effective being able to [throw a high fastball]," said Jackie Bradley, Jr. "What makes the pitches that are elevated a lot tougher to hit is just because, in the back of a hitter's head, he might throw me something soft. So I want to give myself more time, which ends up making you late on the fastball."

"Nowadays, they're swinging at [high fastballs] more than ever," Drew Pomeranz said. "Definitely the curveball helps. When I started throwing more curveballs, they started playing off of each other more. That’s the name of the game these days."

It can be more difficult for hitters to adjust to changes up and down the strike zone than inside and outside.

"Obviously working east and west is important," said Willis, "but guys who can throw a depth breaking ball, it really creates a lot of deception with that fastball up in the zone. It makes it challenging for the hitter to determine where that ball is going to be."

"Once hitters get about 80 to 100 at-bats, I think they have a clearer understanding of where the strike zone ends east and west," manager John Farrell said. "But when you throw a pitch up at the eyes of a hitter, there's an urge to address it."

Porcello's inconsistency this season can be attributed at times to his inability to maintain his two fastballs as discrete pitches. When his sinker elevates or his four-seamer isn't consistently on top of the zone, "visually it doesn't have the same effect on a hitter."

"I've gotten into high pitch counts because I haven't had the separation on the fastballs," he said. "If I'm not doing that, it turns into a battle where you're pumping heaters and guys are fouling it off. You're scratching your head.

"It goes back to that separation. It's a fine line that makes all the difference in the results."

Porcello thought for a moment about the way pitching continues to evolve, musing about how en vogue cutters were just a few years ago, before hitters adjusted to them.

"It's the beautiful part about the game," he said. "There's never an exact answer that always works. It's adjusting and changing."