You could be forgiven if the Minnesota Twins recalling Tyler Duffey on the last homestand didn’t register on your radar.

A lot of things are going on with this team right now — most notably, winning and hitting homers — and the return of a reliever who posted a 7.20 ERA when fans saw him last probably doesn’t get many of them too excited.

But if you think it’s the same Duffey you’ve seen before, you’re sorely mistaken.

Duffey’s early results have been fairly positive — it has only been three appearances spanning four innings — as the 28-year-old righty has fanned five of the 16 batters he’s faced while allowing just one earned run.

A furtive glance at his HR/9 would indicate he hasn’t graduated from last season’s bombing, but that’s just one homer allowed in a small sample size. It doesn’t indicate much, and if the things Duffey has been working on continue to stick, that number will come down quickly.

Duffey is the newest convert to the concept of tunneling.

What is tunneling?

It’s really a simple concept that has picked up steam in recent years with the increased usage of GIFs on social media platforms like Twitter. Tunneling is the idea that the baseball travels down the same path regardless of what pitch it is, only deviating from that plane at a point where a hitter is either unable to differentiate what it is, or unable to react to it.

Basically, for a pitcher like Duffey it’s like throwing his curveball and fastball on the same plane, with the high fastball mixing beautifully with the curve down that is his bread and butter.

Here’s the concept illustrated by Rob Friedman, who goes by @PitchingNinja on Twitter:

So again, where this comes into play for Duffey is when he can throw the curveball and fastball out of the same tunnel. Anything down out of the same tunnel will work because the curveball will be basically unhittable, but it also allows Duffey to work up in the zone because hitters have to stay honest to velocity on one end and break on the other.

Duffey said it’s a concept he’s heard a lot about in recent years, but nobody really had explained it to him prior to this spring.

“(I’ve) been hearing it for I guess a couple of years now, I guess the phrase itself,” Duffey said during the team’s last homestand. “But now it’s more of me understanding of what I was doing at times, and repeating that. I think what the problem was that it was presented as ‘We’ve gotta work on tunneling’ but it wasn’t fully explained to me. Describing that we’re going to throw heaters up because the reason we’re doing it is the breaking ball plays better. If you go fastball down, you can’t throw the breaking ball at the guy because now it changes their eyes and they don’t bite. It’s more of understanding what it actually meant versus just saying ‘Throw ‘em in the same spot.’ That’s not the same thing.”

Duffey said it wasn’t that hard for him to buy into the concept, but it was difficult to stomach a tough spring training performance in Fort Myers because he was walking more hitters than he was comfortable with.

In 7.2 innings in big-league camp, Duffey allowed six earned runs — including three homers — in 7.2 innings (7.04 ERA) with eight strikeouts and six walks.

Those struggles were a necessary evil, though — at least as far as Duffey is concerned.

“For me, yes, because I was a sinkerball guy forever,” Duffey said of the adjustment this spring to working up in the zone. “I was down in the zone in the 4-spot with the fastball down and in — down and away to a righty — and I was leaving it in the bottom corner of the zone like (Kyle) Gibson. And now it was like ‘Hey, I gotta change my sights.’

Sep 23, 2018; Oakland, CA, USA; Minnesota Twins catcher Chris Gimenez (46) fist bumps with Minnesota Twins relief pitcher Tyler Duffey (21) after getting Oakland Athletics designated hitter Khris Davis (not pictured) to pop out during the eighth inning at Oakland Coliseum. Mandatory Credit: Neville E. Guard-USA TODAY Sports

“So for me, it was finding a happy medium because I was missing really high. Then I had to bring it back down, but I also had to realize there are bigger guys, so you have to go higher than normal. It’s just like a normal scouting report, except you have to know where they can hit the high ball and find above that to pitch. Then you throw breaking balls off that, and the rest takes care of itself.”

There’s no specific path a pitcher needs to take to tunneling, since Duffey agrees it’s kind of a chicken-and-egg scenario where he can mix and match his fastball and his curve in whatever order he sees fit.

“It’s definitely both ways,” he said. “If you flip a breaking ball and the guy maybe leans on one, and then you throw the fastball on that same plane, if they’re leaning they’re really in trouble. If they’re not looking for it, it’s at least going to get them off the plate in the worst case. You’ll get a swing and a miss or a weak pop-up, whatever. That’s the name of the game, getting soft contact.”

Working up in the zone carries the natural caveat, or perhaps worry, that a pitcher’s groundball rate will crater. And perhaps that’s nature versus nurture, but it’s something that has fluctuated fairly significantly in Duffey’s career.

The idea of wanting to induce grounders from a pitcher’s standpoint is that they rarely go for extra-base hits, and a capable infield defense can vacuum them up for easy outs. Fly balls can be a bit more tricky — especially in this advanced launch angle era — though the mitigating factor there can be popups.

Duffey hasn’t induced a popup yet in the big leagues this season, but the Twins staff has induced a popup rate of 15.6 percent this season — far and away the best in baseball. Oakland is second, more than 2.0 percent behind (13.3 percent).

So what will this new-found reliance on pitching up in the zone do to Duffey’s groundball rate? He’s not totally sure. It’s at 55.6 percent this year, it was 34.1 percent last year and for his career, it’s 47.5 percent.

A good rule of thumb is that average is roughly 45 percent.

Four innings doesn’t seem like a lot for batted-ball rates, but groundball rate actually stabilizes fairly quickly. According to the I sample-size article posted by Steve Slowinski on Feb. 18, 2010, groundball rate stabilizes at 70 balls in play.

Duffey’s still a little way off from that, but it’s something to monitor as his innings total racks up.

“(Honestly, it’ll) probably get rid of it,” Duffey said with a mockingly exasperated sigh in regard to his groundball rate. “I think my curveball has always had a decent one. I don’t know the numbers off-hand. I mentioned that to I want to say it was (pitching coach) Wes (Johnson) and (bullpen coach Jeremy Hefner) Hef at the beginning of the spring, and they said you’ll get groundballs with the curveball anyway.

“So you don’t necessarily need to worry about it. So with the breaking ball I’m not truly throwing up; it’s about starting versus finishing. It still plays to the bottom of their bats, which is the name of the game. With the fastball, if those are weak popups those are easy outs. Three things have to happen on a groundball, one thing has to happen on a pop-up. Well, I guess you could say four — get to the ball, field it, throw it and catch it at first base. Popups are easy outs, so as long as they stay in the yard, that works.”

Apr 16, 2019; Minneapolis, MN, USA; Minnesota Twins pitcher Tyler Duffey (21) delivers a pitch during the eighth inning against the Toronto Blue Jays at Target Field. Mandatory Credit: Marilyn Indahl-USA TODAY Sports

Another thing Duffey wanted to focus on was getting more strikeouts.

Duffey was a Terry Ryan product out of Rice University, going in the fifth round of the 2012 draft as a college reliever with just one start under his belt. Like most pitchers drafted that high, strikeouts came by the bushel in college — 11.1 per nine innings over just over 150 frames — but that depreciated significantly in the minor leagues (7.7 K/9) and in the big leagues (8.0).

The righty is aware of the stigma the Ryan Twins had about strikeouts, and has been diligently working to flip the script on his narrative.

“I know, and that’s why I threw sinkers,” Duffey said of how his pitch mix was affected by coming up in the era he did. “It was ‘Get ‘em out in three or less pitches.’ It worked if you got the soft contact. If you had the above-average defense, which I had for so long in the minors. I came up with a lot of these guys all through it and so it worked, but once teams adjusted to that and started hitting it in the air, well that kind of gets rid of your infield defense. It’s the name of the game — they change, we change. It never stops.”

The significance of this seismic shift in ideology is not lost on Duffey, but he’s nothing if not appreciative of coming to the big leagues when he did — even if he’s never been a key cog in any particularly good Twins squads.

“I’m definitely better for having come up when I did,” Duffey said. “I had some really good coaches throughout the minor leagues. Gary Lucas, Ivan Arteaga — I had him three or four different times and he was great — Marty Mason, Stu Cliburn and even Mike McCarthy down there now. Pretty much top to bottom, even with the changes it’s good, new information.

“Now with all the minds we have here, it’s become really easy to stay up with the times and learn what the buzzwords are, what they mean, this is why we’re doing this and that. There are numbers and evidence to it, which makes it really easy to get behind.”

It’s easy to see why a shift like this would feel so significant for a pitcher so ingrained in the old-school Twins way — especially with so few of those pitchers remaining — but Duffey feels like he’s up to the task of adjusting on the fly.

“I feel like I have the potential to be a strikeout guy,” he said. “I can strike people out, but more on a consistent basis. I don’t even know what to compare to, but at least one an inning. You can come in and punch out a guy if you really need to, and if you do it quickly, you can be efficient and go deep as well. So just trying to do that, and getting quick outs ultimately.”

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