On April 28, the Phillies and Braves squared off for the second game of a series, just as they will on Friday. Back then, both teams trailed the Mets in the NL East, but a week later, they would occupy the top two spots in the standings, and they’ve jockeyed for first in the past several months since then. That April matchup offered a good glimpse of a particular talent that has helped keep the two teams in contention: their backstops’ ability to snare extra strikes.

In the second inning, Braves catcher Tyler Flowers took a 2-0 fastball that Pitch Info assessed as only 41 percent likely to be called a strike. Home-plate umpire Kerwin Danley raised his right hand regardless.

Flowers then swung through a curveball and, with the count 2-2, took another borderline pitch. This one was slightly closer to the strike zone, raising the odds of a strike to 81.9 percent, but Phillies catcher Jorge Alfaro left little to chance. Just as he had on the 2-0 delivery, Alfaro tugged the pitch up past the 6-foot-4 Flowers’s knees and got the strike call, then almost skipped off the field as Flowers headed back to the dugout, dismayed.

The Braves’ backstop didn’t have to wait long for revenge. On the first pitch to Alfaro in the following inning, Flowers returned the favor and pulled up a low pitch. The odds of a four-seamer in that count and location being called a strike were only 14.8 percent, but Danley, duped again, gave the Braves the call.

By the end of the fifth, the Braves were up 4-1. The score stayed that way thanks in part to an even finer Flowers frame job to quell a Phillies rally in the eighth, when an exasperated Rhys Hoskins went down staring at a 9.7 percent likely strike.

On the night, the defeated Phillies, in 77 called pitches, got two more strikes than expected. The victorious Braves, in 78 called pitches, got four. According to Baseball Prospectus, Flowers has amassed the most runs from framing of any catcher this season despite starting only 65 games behind the plate. Alfaro, who’s started 95 games at catcher, ranks fourth. Framing has been a feature or bug built into baseball from the beginning, and while it’s not, by any thorough reading of the rulebook, explicitly illegal, the notion that the strike zone can be stretched by backstop sleight of hand strikes some spectators as unsporting. While unequal calls won’t be banished until computers call pitches, there is good news for fans who feel that framing is unfair: The separation between teams in catcher-receiving skills appears to be smaller than ever before.

References to pitch-framing date back to at least the 1950s, and probably before. An organizational instruction manual prepared by the Brewers in 1982 advised catchers to catch possible strikes with “a minimum of body movement” and “very smooth hand action,” noting that “good framing technique will usually get you more marginal pitches.” And in his 1989 book The Diamond Appraised, trailblazing sabermetrician Craig R. Wright wrote that “the mark of the master is the illusion whereby balls become called strikes,” arguing that “learning to catch the ball so it looks like a strike may do more toward preventing runs than throwing out the extra base runner once a week that is the difference between the best- and worst-throwing catchers.”

If awareness of framing technique dates back so far, it’s only natural to wonder why anything would be different on a league-wide level today. But the past decade has brought a dramatic development: the advent of tracking technology that can pinpoint each pitch’s precise location relative to the borders of the strike zone, allowing analysts to discern which catchers consistently get calls on suspect pitches. Prior to the PITCHf/x era, which began in all big-league ballparks in 2008, evaluating framing performance was, as Wright noted, mostly “speculation and theories in the dark.” Although Wright and some subsequent researchers showed that certain catchers displayed a persistent knack for lowering run totals, there was no way to isolate or accurately quantify the impact of their receiving skills alone. As a result, Wright wrote, “most baseball experts don’t even try to weigh this aspect of a catcher’s defense; instead, they focus solely on the things that they can see: agility behind the plate, the number of passed balls, and, above all else, the catcher’s throwing ability.”

Longtime catching instructor and current Rockies scouting and player development assistant Jerry Weinstein concurs with Wright’s assessment in The Diamond Appraised. “It used to be ‘block and throw,’ and basically catch the ball instead of picking it up after it stops rolling, so how you caught it didn’t seem to be a priority,” Weinstein says. “Now we’re understanding [that] how you catch it is really critical.” The difference is today’s technology and the detailed data it yields. “It’s the old deal, you can’t improve it unless you measure it,” Weinstein continues. “And nobody was interested in improving it because they didn’t realize the importance until people started measuring it and they started showing them how important it was.”

The first public framing research derived from tracking data appeared online in 2008, and at least one front office identified framing’s previously underrated impact by early 2009. But knowledge of framing didn’t really reach the mainstream until analyst Mike Fast blew the lid off the almost-secret skill in a September 2011 study at Baseball Prospectus. Soon, teams—including the Astros, who hired Fast in early 2012—were making a concerted effort to improve their framing performance. In 2008, the first year for which we have PITCHf/x-based framing stats, the range in receiving value between the best and worst teams was more than 90 runs, or roughly nine wins. Even in 2011, the range remained nearly 90 runs. But in 2012, the first season after Fast’s piece was published, it shrank to a little more than 60 runs.

While the range and variation of framing performance fluctuates from year to year, the trend has continued to be downward, with 2018 on track to be the most compressed year yet. This season, the separation between the best and worst framing teams may be less than half of what it was a decade ago. The graphs below show the steadily decreasing range and variation in team framing runs and Called Strikes Above Average (CSAA), a rate stat that measures a catcher’s impact on garnering extra strikes.

We can see a similar decrease when we look at the average framing runs total of each season’s top 10 and bottom 10 catchers with at least 2,000 framing opportunities, scaled to 7,000 (roughly a full season’s worth for a starting catcher).

Early in the PITCHf/x era, it was possible for framing leaders like José Molina and laggards like Ryan Doumit to produce strikes at a rate that would add or subtract 40 runs or more to their teams over a full season through receiving alone. (Including his play-by-play-based estimated framing totals from the pre-PITCHf/x years, Molina finished with 202 runs from framing in 15 seasons spent primarily as a backup; Doumit, maybe even more incredibly, subtracted 167 framing runs in only 10 seasons of part-time play behind the plate.) Today, it’s unheard of for catchers to stand out so far from the pack in either direction, largely because the Molinas and Doumits of yesteryear didn’t go unnoticed. “As a result of those stats, people are seeing the importance of receiving, framing, catching, etc., and so now they’re looking at the best guys, they’re seeing what they do, they’re modeling those traits with their catchers; so they’re spending a lot more time on the receiving piece of the equation,” Weinstein says.

The best receivers don’t rate as far above the average because their competition keeps improving. And the worst receivers don’t rate as far below, both because catchers who struggle with receiving devote themselves to improving that aspect of their performance and because teams won’t give playing time to catchers who have no aptitude for framing. Molina himself is part of this process: As the Angels’ minor-league catching coordinator, he’s tasked with training more catchers who can do what he did. As one major league general manager says, “The ‘average’ framer is now better than he was five years ago because clubs are able to coach him to get better. Second, the really bad framers who haven’t improved—even with the aforementioned coaching—no longer get major league jobs. They’re either playing in Triple-A as an up/down guy or they’re moved to another position.”

Flowers and Alfaro are examples of the former effect in action. The 32-year-old Flowers, who also led the majors in framing runs last year, was always an above-average framer, but he’s been more than twice as effective on a per-opportunity basis from 2015 on than he was prior to that, which he says is “definitely not a coincidence.” He credits the change to a graphic on a TV broadcast that listed baseball’s best framers—Flowers not included. “The first time I saw those numbers, I realized, ‘Shit, I’m not as good as I think I am,’” he says. “That’s when I kinda went to work studying the guys that were at the top of that list.” Flowers watched video of the most successful framers and adjusted his setup to get lower to the ground, enabling him to receive low pitches smoothly in spite of his height. He says he has seven different setups that he chooses from depending on pitch type and location and whether he’s getting calls. For instance, he might drop his right knee down with runners on or two strikes (which gives him more freedom to handle low pitches or move to his right); drop his left knee down with nobody on and fewer than two strikes (which frees him up in case of an “accidental sinker” from a righty or a lefty accidentally cutting a fastball); or adjust the angle of his upper body to affect the umpire’s perception (by pressing his chest forward and down to make the strike zone look lower).

“The really bad framers who haven’t improved—even with the aforementioned coaching—no longer get major league jobs.” —Major league general manager

When Flowers gets back to the clubhouse after a game, he pulls up stats and video on his iPad to examine what worked and what didn’t. “The last couple years is even more fun because I get, essentially, real-time information,” he says. “Right after the game ends, I can see every pitch and I can see the percentage of the time it’s called a strike and called a ball, and I feel like that’s even better for me because it’s so fresh in my mind.”

Flowers is hyperaware of his framing performance: His goal coming into the season was to top the BP leaderboard again, and he returns to it often to confirm that he’s holding off the rest of the field. He notes, though, that while he is still in first, he and the other elite framers aren’t as far above the average as they were even last year. “I think we’re gonna start to see it trend down like it is,” he says. He speculates that that could be partly a product of league-wide trends in pitching: Pitchers are throwing more breaking balls and more pitches outside the strike zone, and when they throw fastballs, they’re often aiming up. Flowers says it’s harder to get calls at or above the top of the zone than the bottom, and preparing for a pitch up can compromise a catcher’s ability to present a pitch that ends up low. But beyond that, there’s the copycat problem. Just as Flowers studied video of strong framers from a few years ago to refine his own approach, other catchers are now taking cues from him and other model strike-stealers. “A lot of catchers [are] going down to one knee,” Flowers says, adding, “There’s been a lot of guys jumping on that bandwagon.”

One need look no further for an example than the first GIF of Alfaro above: There’s the Phillies backstop dropping to his left knee with the bases empty and fewer than two strikes, just as Flowers described—and, in this case, costing Flowers directly. That’s not a coincidence either. First-year Phillies bullpen catcher/receiving coach Craig Driver says the team’s plan this spring was to help Alfaro improve his framing performance at the bottom of the zone, where most of the top-rated receivers excel. “We wanted to devise as much of a plan to get him low and work under the baseball as we could,” Driver says. “So one of the things we encouraged him to do a lot was catch off one knee.” Driver says setting up lower has benefited Alfaro by bringing his eyes closer to where the ball is going to be, making it easier for him to pull low pitches up into the strike zone and saving some strain on his knees compared to squatting.

Driver acknowledges reviewing video of baseball’s best catchers to pick up on and impart proper techniques to the team’s catchers. “Having that quantitative view of where guys stand really gives you the ability to study the best and pick up traits that may or may not help your guys,” Driver says. “I’d be crazy to say, ‘All you guys are going to catch like Tyler Flowers,’ or ‘All you guys are going to catch like Jeff Mathis or Austin Barnes’—whoever it may be. But if we can pick up some traits that maybe helped them in one isolated area [where] one of our guys struggles, we’ll absolutely look at trying to figure out how we can make our guys as good as we can.”

Alfaro doesn’t seek out stats and queue up his own highlights and lowlights like Flowers does. Instead, Driver meets with him once a week or once a series to go over what he’s doing well and what he can keep tweaking. The two also go through a pregame framing-practice routine in which Driver uses a pitching machine to fire fast pitches for Alfaro to frame, rather than throwing pitches at slower speeds that wouldn’t prepare Alfaro for in-game conditions. “Most guys can manipulate the baseball at a pretty high level when I throw it to them at whatever—50, 60 miles an hour—that I’d be throwing BP at,” Driver says. “But being able to simulate something that’s a little more game-like has been really big for us.” The two have also worked on conditioning Alfaro to position his hand on the optimal plane to present each individual pitch type, rather than trying to receive distinct offerings the same way.

Alfaro has been a below-average blocker this season, and he hasn’t distinguished himself at restricting the running game, but he’s among the league leaders in the column that matters most. Although Driver and other coaches work with Alfaro on other aspects of the position, Driver says that “receiving’s going to be done the most of any of the three main catching skills.” That’s not something that a catching instructor would have been likely to say in the pre-PITCHf/x era. Then again, a catching instructor in the pre-PITCHf/x era likely wouldn’t have been called a “receiving coach.” And Alfaro’s effort has paid off: Among the 48 catchers with at least 1,500 framing opportunities in both 2017 and 2018, only Rockies converted catcher Tony Wolters has improved his CSAA relative to last season by more than Alfaro.

“A lot of catchers [are] going down to one knee. There’s been a lot of guys jumping on that bandwagon.” —Tyler Flowers

Granted, experience and greater familiarity with the Phillies’ staff might have helped Alfaro’s receiving regardless, but it’s clear from Flowers’s and Alfaro’s recent results (and several other past success stories) that catchers can consciously refine their framing. Weinstein, Flowers, and Driver all agree that while body shape, wrist and hand strength and speed, lower-half flexibility, hand-eye coordination, and other physical factors affect framing, the gaps between teams and between players are closing because receiving is, at least to an extent, a teachable skill. It’s easier for a player who’s already capable of catching major league pitches to catch those pitches better than it is for a slow player to run fast, a soft-tosser to throw hard, or an easy out to learn how to hit. “I think everybody can get better, and not just a little bit,” Weinstein says.

Amid this heightened focus on framing, the league-wide strike rate on taken pitches is no higher in 2018 than it was at the dawn of the PITCHf/x era in 2008, but pitches were thrown in the strike zone at a higher rate back then than they are today. On pitches taken inside the rulebook strike zone, the called-strike rate has climbed from 74.7 percent in 2008 to 87.3 percent this season. That’s partly—or maybe even largely—a product of umpires getting graded on their accuracy and hewing closer to the strike zone’s rule-book-dictated dimensions; it’s difficult to determine how much of the shrinking variation among catchers can be traced to the shrinking variation among umps. But a better caliber of catcher should mean more called strikes, and more called strikes should (among many other factors) contribute to more strikeouts, which we’re seeing year after year.

Flowers notes, though, that although the rising tide is lifting all backstops, framing greatness requires the right tools, the right teacher, and, most importantly, the single-minded pursuit of strike calls that makes him keep pulling out his iPad and pulling up BP. “If you’re not into it, you’re not gonna be very good,” Flowers says. “You might be able to get by just on raw talent, which I think some guys do, but I think the guys you see toward the top each year, I think they’re into it. They see the real value of it. … It’s got to be essentially a 24-7 thought on your mind and a desire to get every single pitch that’s close to the zone.” One almost hopes that for Flowers’s sake, his career wraps up before the robots umps arrive and take all his framing fun away.

Stats are current through Wednesday’s games.