The success of the 2022 Seattle Mariners has flowed in large part through their rookie sensation, Julio Rodríguez, and their once-more spectacular bullpen. The 2021 core returned many of its most important pieces, namely Paul Sewald, Diego Castillo, Andrés Muñoz, and Erik Swanson, but trades and injuries have sapped them of several vital performances from their previous season, creating openings for players like 28-year-old rookie RHP Penn Murfee. The sidearming righty was selected 988th overall in 2018, in a round (33rd) that no longer exists in the MLB draft. His journey is fascinating, but at this point he’s just shy of 50 innings pitched for Seattle, sitting at a 2.36/2.83/3.60 ERA/FIP/DRA and a delectable 59/65/82 ERA-/FIP-/DRA-. He has been utterly brilliant, and his pathway to doing so has been delightfully uncommon.
The simplest, most important thing to understand about Murfee’s success this year is that his slider has been otherworldly. If you’ve watched him, it’s obvious, and it’s rightfully his primary pitch. When Murfee spoke with our Isabelle Minasian recently, he discussed the progression of his grip on the slider, which did not always have its monstrous current shape:
“The slider grip has changed quite a bit over time. When I first started throwing it I was way up in the horseshoe, like a 12-6 curveball sort of grip. I wanted the effect of the four-seam spinning end over end perfectly. But for whatever reason I’ve drifted further over to the train tracks (Ed. note: the narrow point of the seams, commonly where a two-seam fastball is held). And a lot of guys have kind of figured out that gives you more horizontal sweep, and I just think that over time my eyes were telling me - and where I was comfortable with the grip - I could see it, I wasn’t even really thinking about it but those incremental incentives kind of just stacked up over time to where I was like ‘Okay, I like how it moves, seeing it with my own eyes more as I (my grip) drifted down.”
As a minor leaguer, Murfee often had success despite middling velocity, leveraging a funky delivery and solid secondaries into some solid numbers, even as a starter. But old for his levels and dealing from an arm slot at least traditionally viewed as liable to over-exposure in starting roles, Murfee shifted to the pen full-time, and as he’s gone his cutter and breaking ball took a back seat to his ever-changing sweeping slider. Jake Mailhot wrote for FanGraphs about Murfee’s immediate success due in large part to the slider, as he is wont to do, and it is borderline mandatory reading if you haven’t yet before continuing. To capture the gist, Murfee’s slider is incredibly effective because it is so flat and so extreme in its horizontal movement, akin in many ways to the pitch that has helped make M’s relief ace Paul Sewald so successful. When you wonder if I’m trying to overthink things later, let this be your checkpoint, hit F5 and quicksave, and return to this respawn point: Murfee’s slider is his best pivtch. But his fastball is perhaps what’s most interesting.
Murfee’s four-seamer is bizarre. It averages 89.2 mph on the season, good for 6th percentile in MLB, and yet this pitch he throws roughly 40% of the time has been reasonably effective. It has a Called Strikes plus Whiffs rate (CSW%) of 27.0%, a tick or two below average but within the “fine” range. Part of this, and arguably most or all of this comes due to Murfee’s delivery, wherein his low sidearm release allows him to pump his four-seam at a nearly flat vertical approach angle (VAA) that makes it harder for hitters to handle up in the zone. If Murfee throws to the upper parts of the zone or above to a taller hitter, he may literally be throwing fastballs that are on a rising pathway from his hand, though Murfee’s ultra-low release is still more Steve Cishek than Tyler Rogers. And yet, what fascinated me enough to want to know anything I could about Murfee’s fastball was this tidbit from the endlessly useful charts of Alex Chamberlain, via data in large part accessed through Baseball Savant’s boards:
Why is Murfee throwing a dramatically less “efficient” spinning four-seam fastball than anyone else in MLB? Is he even throwing a four-seamer technically at this point? And is there any potential/intentional benefit to throwing a pitch that spins quite a bit, but actively does not utilize that spin in its movement towards the plate?
When Isabelle asked Murfee to talk through his fastball grip, his answers were as interesting as I’d hoped it might be. During his time in Triple-A Tacoma last year, it appears something changed. “I think that last year my pitching coach Rob Marcello came to me after one outing and was like ‘Hey, I don’t know what you did but your fastball went from being one of the worst that we had to to, you know, it really stood out,” said Murfee, “I couldn’t really tell you, it just happened overnight and I just kind of stuck with it.”
Marcello is sadly now with the San Diego Padres, but his influence carries on. Here’s a typical Murfee heater, a four-seamer in his average range on the fastball of 88-90 mph:
Juxtapose that with the slider, which is, as advertised, a sweeping horizontal monstrosity that most hitters can’t handle in the slightest.
So surely these pitches, which Murfee has noted have required frequent tweaks and adjustments over time, are dramatically different in terms of what it takes to produce them, right Penn?
“It’s kinda the same grip. It’s the same positioning with my fingers and my thumb, just on a different part of the ball ... I’m about halfway in between [the horseshoes and the train tracks] on my slider, and then with my fastball I’m going across the horseshoe, just like a normal four seam fastball, but it’s a little off-set. So like if you watch Mariano [Rivera]’s how to throw a cutter video on YouTube, I kind of do the same thing where I tilt it a little bit pre-set.
Okay, now we’re making progress. Murfee’s fastball is modeled off the cutter of the greatest reliever of all time. If we look at the spin of both pitches, it seems to be working.
In terms of spin, his fastball and slider are almost identical! We can see the slight “pre-set tilt” come into play as he describes it, yet both pitches are essentially coming out the same, with one moving feet and the other flying almost entirely straight and then sinking somewhat late. Despite having the spin of a cutter, Murfee’s fastball is a movement-limited option that more accurately represents descriptions of the fabled gyroball. The pitch made famous in Japan by a few specific trainers and pitchers is essentially a deceptive pitch based on spin and lack of movement in spite of what it suggests. Gyroscopic spin is, in the terms of a layperson, spin that occurs but is perpendicular and not directly as impactful on the flight of the ball. There are two classic examples of this type of spin, which Penn and Isabelle contextualized helpfully in their discussion on what Murfee is aiming for upon his release of the ball:
“In my fastball, I guess I just want to feel like my middle finger gets a lot of the pressure (It shows! His middle fingernail has like a permanent blood bruise callus underneath the nail, the trademark of a prolific slider-thrower). My fastball spin is weird in that I kind of throw like a bullet spinning fastball.” [Isabelle - “It’s like throwing a football?”] Right, right!”
“So for me that all comes from my middle finger. If I start to get my pointer finger involved more I’ll flush the ball up more and get more armside run and I don’t want that. I want my hand to still be kind of pointed up and I just want to be feeling this so I can spin it like that.”
Therein, then, we have it. This is not mere happenstance, but an intentional effort by Murfee to throw his fastball in a way no other pitcher in all of Major League Baseball does. His “four-seam” fastball spins like a cutter or slider, and yet it is one of the least horizontally mobile four-seamers in all of baseball. Per Murfee, it’s something the organization continues to encourage him on, as it is “really unique” and “weird”. For his own efforts, he continues to discuss and fine tune things whenever possible, talking with his fellow pitchers, catchers, and when possible, opposing batters.
“I’ve talked with a number of people - hitters too, especially that I’ve faced. It’s kind of been figuring out what doesn’t work more than anything else. I just wish I could face myself or catch myself and see how it comes in, but I trust the information I was given. The org has their portal and their analytics that they look at and I trusted that information when I got it.”
Murfee also mentioned discussions with other players around the league, including a nod of appreciation to teammate Ryan Borucki for introducing him to PNW native Adam Cimber, a fellow sidearm/submariner who Borucki knew well from their time as teammates in Toronto. Cimber’s success comes from a two-seam/slider combo, which employs an excellent example of a concept called “spin mirroring,” an extension of the concept of “tunneling.” In essence, tunneling is simply throwing two (or more) pitches with a consistent release point that not only come out looking similar, but follow similar flight patterns to the plate. Spin mirroring expands on this, pairing pitches traveling in opposite directions with similar spin rates but mirrored spin directions to create additional deception for the hitter and reduce reaction time. A classic example is a four-seam fastball with pure backspin and a 12-6 curveball with pure frontspin, the combo that made Gerrit Cole a perennial Cy Young contender among many other standouts. Two-seam/sinker and slider is another common mirrored pair, but what Murfee seems to be employing is a different trick altogether.
By throwing his sweeping slider, Murfee can sometimes fully erase hitters without another trick. But when he does go to his fastball, Murfee is, in his own words, throwing almost the same exact pitch as the massive sweeper. Instead, however, despite nearly the same spin and a football spiral, supinated release, Murfee is throwing a nearly totally straight fastball that only suffers a bit more late sink than a typical four-seamer. It is, essentially, a firm gyroball, spinning just the same as the massive sweeping slider 8-10 mph its lesser. This near-match in spin creates a significant boost in deception that seems to help both pitches play up. It’s hard to find precedent for a player like Murfee in the Statcast era - even Steve Cisek used to throw harder - but his continued curiosity and efforts to improve have helped him become a lynchpin in Seattle’s playoff-caliber bullpen no matter how unprecedented he may be.