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Peoria, Arizona —— The Seattle Mariners have three right-handed power relievers as part of their contingent at the Arizona Fall League right now for the Peoria Javelinas: Art Warren, Darin Gillies, and Matthew Festa. And in a way similar to a phenomenon I saw earlier during the summer with the Mariners’ High-A club in Modesto, all three are showing off power stuff out of the ‘pen in a way that will continue to draw them attention — and no doubt some chatter from other organizations — over the winter.

I want to dive a bit deeper into that question about the future of these three, but before we do it let’s contextualize with some video of each guy from this week in the Arizona Fall League. (Reminder: click here and subscribe to the Baseball Census YouTube channel if you like the work we’re doing and you want more videos like this one.)

Darin Gillies, RHP, Seattle Mariners

The Arizona Fall League marks my first time seeing Darin Gillies pitch in 2017. The righty, who spent all summer with Double-A Arkansas, has some giddyup to his fastball in a way similar to Art Warren, but appears to only throw one breaking ball compared to two from both Warren and Matthew Festa. That said, it’s an above-average breaking ball with a power slider feel and some heat to it, and yet it also has legitimate curve break at 11-to-5 with very good depth. Gillies has feel for the pitch and likes to use it, and it’s a good look against both righties and lefties with the nearly vertical drop and some command to both sides of the plate.

He should start 2018 at Triple-A Tacoma, and depending on depth and need, Darin Gillies will almost certainly be a part of the big league bullpen conversation by the end of next summer, if not sooner. Long term, my hunch is he doesn’t have quite the late-inning ceiling of a guy like Warren, and winds up working as a middle relief 6th/7th inning type of arm.

Art Warren, RHP, Seattle Mariners

We’ve seen Art Warren quite a bit in both 2016 and 2017, and he has blossomed into a significant power relief arm that has a legitimate big league high-leverage ceiling. Our most recent look at him before the Arizona Fall League involved a deeper dive into his curve/slider combo; before that we also spoke to him about what changed this year in his development, and got an early May look at the powerful righty up in Modesto before anyone knew how good he might be.

Of these three pitchers, Warren has the most value and the highest ceiling. I believe he’ll throw even harder next year than he does now, with a legitimate shot at sitting 97-99 mph with the fastball assuming good health and good fortune. He’s got the physicality and frame ideal for late inning work, and his slider and curve are both well above-average and distinct enough from each other that he can mix and match against hitters on both sides of the plate without worrying about being a late-inning matchup liability out of the ‘pen. He’s a high-adrenaline guy and still working to channel that all the way to the plate, so his fastball command could use modest refinement to keep from jumping out of his hand and sitting too high in the strike zone when he’s really wound up. That’s a relatively small adjustment that will come in time, and one he can mostly get away with for now thanks to plus-plus velocity and the feel for those two breaking balls.

Matthew Festa, RHP, Seattle Mariners

The most polished true pitcher out of these three power guys, Matthew Festa put up absurd numbers in 2017 before coming to the Arizona Fall League: a 99:19 strikeout-to-walk ratio and a .228 opponents’ batting average over 69.2 bullpen innings for Modesto landed him a California League All-Star nod and, for much of the year, the Nuts’ closer gig. Like Warren, Festa flashes mid-90s heat with two breaking ball looks, and even though his command is generally the best of the three arms here, it’s ironically been off a bit in both of the last two outings I’ve observed — last month during the Cal League playoffs and in the above video outing at the Arizona Fall League. That’s anecdotal, of course; Festa has the most reliable and consistent mechanics of the three, and he’s relatively low-maintenance there with some polish to his sequencing and stuff that’ll help push him into the big league conversation by the end of next year, or early 2019.



It should not be a coincidence to you that the Seattle Mariners sent three very similar right-handed relievers all to the Arizona Fall League together this month, because I believe there is a near certainty at least one of them will be traded this winter. The big league club wants to win right now, and after a disappointing 2017 where they never quite got things going like they’d expected, I imagine they’ll be open to making a move or two to address 25-man roster shortcomings and push to win immediately in 2018. To that end, there’s little doubt in my mind that at least one of these three — Art Warren, Darin Gillies, and/or Matthew Festa — will be packaged this winter into larger trade deals that’ll have big league ramifications.

Warren ultimately has the highest relief ceiling of the three, and I think he’s got a shot at a job as a big league closer one day. He’d be the most valuable of the three in a trade, then, even though he likely won’t have a big league impact until early 2019. Darin Gillies, on the other hand, is the closest to the big leagues of these three and may have an inside track there if another organization is internally high on him and believes he can make an impact soon at the big league level. Matthew Festa is the best true pitcher of these three guys, and while there’s some middle/late-inning relief value to be gleaned from his power arsenal, I could honestly see a team taking a chance on putting him in a Double-A starting rotation next year to see how his command profile and deep arsenal play out in that larger role. That would take a trade partner with some vision who is willing to take a chance, though, and it’s probably most likely Festa, like the others, remains an attractive late relief prospect.

As attractive as double-plus velocity may be from the outside looking in, organizations have a better handle on how to develop back-end relief arms now than they ever have before. Hell, the Seattle Mariners have already squeezed considerable value out of these three under-the-radar guys in particular, none of whom you’d figure for a likely future AFL participant had you looked at their profiles a year or two ago. Gillies started 28 games in college and was a tenth round swingman starter/long reliever in his rookie summer before transitioning completely to the bullpen in 2016. Warren was a late-round, small school arm who spent 2016 as a below-average starting pitcher with absolutely no inkling that this type of power could come from his game. And Festa was also a small school diamond in the rough who started for his entire college career, and for most of last summer, before making the bullpen jump six months ago in Modesto.

That’s all to say this: the Seattle Mariners have three guys here who, through hard work and a little luck and a lot of player development and some good fortune and perfect timing found themselves particularly apt to bullpen work. There will be more arms like these coming through Seattle’s system in the next few years, too — starters that wash out, hard-throwers who can’t quite get their command down — just as was the case with reliever Lukas Schiraldi before the club shipped him off this summer as part of another big league trade package. There’s no sense in trading players just to make trades, but with these three right-handed power relief arms in particular, all of whom are at more or less the same stage in development right now, why not move one (or two) if you feel like it can make you stronger in other areas that’ll help the push in 2018? Sell high on one or two of ’em, put the finishing development touches on those remaining, and go into 2018 with a better 25-man roster than you had before.

The Seattle Mariners aren’t strangers to making a lot of moves under their new front office regime, and I’m not sure why they’d get gun shy about wheeling and dealing now, especially considering the high expectations and the club’s inability to meet them in 2017. As it does for so many players every year, I think the AFL is nothing more than a trade showcase for Warren, Gillies, and Festa, and I’m sure the Mariners will receive calls on each one over the next few months. Without question, the pro scouts of 29 big league organizations are hard at work in Peoria this month trying to get a good read on these three arms.

No point in picking out trade partners and trying to match specific needs with other organizations right now, but the broad idea here remains: Art Warren, Darin Gillies, and Matthew Festa have all made themselves attractive relief prospects with future big league value. I believe there’s a very, very good chance the Seattle Mariners sell high and package at least one of them in a larger trade soon after the Arizona Fall League schedule is completed.


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  1. […] and I mentioned it in the video, too, so how about we show you Art Warren working on his craft out at AFL from a behind-the-plate viewpoint, too? Below, this video from late October in Scottsdale will give you a good visual reference to […]

  2. […] high-leverage role long-term; compared to some of the Seattle Mariners’ better relief prospects (Matt Festa, Art Warren), Seth Elledge is at a tick or two behind. Video Below, game video to supplement our […]

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