Baseball America exposes an unexpected weakness in Mariners' pitching pipeline

Though the Mariners have struggled to find consistent offensive productivity for years, their pitching has become a point of pride for the organization. Unlike many teams, which have a big disparity between the abilities of the best arm in their rotation and the worst, Seattle's starting pitchers have typically been pretty solid and more importantly, homegrown. With Luis Castillo now with the White Sox, every player in Seattle's rotation was drafted by the organization.

This string of success is the reason why the team's starting pitching depth has been sought after for the past several offseasons. However, despite its stellar reputation, some cracks are starting to show. In 2026, Seattle starters combined for a 4.05 ERA, 10th in MLB. Even after trading away Castillo, their worst starter, the Mariners rotation posted a 4.49 ERA over the last two months of the season, 23rd in MLB.

It's not the only thing that fell short of its lofty expectations and to many, this fall-off may not have even been obvious with everything else that went on. Moving forward, some may expect things to return to business as usual, but others are hinting the reign of dominant pitching in Seattle may soon be coming to an end.

Baseball America ranks the potential of the Mariners' pitching prospects dead last

Baseball America recently released their Statcast rankings of all 30 farm systems, using minor league data to rank teams based on things like exit velocity, swing decisions, and other advanced metrics.

On the pitching side, they used a proprietary Stuff+ model to evaluate pitchers based on intrinsic characteristics such as velocity and release point. Other publications like FanGraphs also measure Stuff+, but each model is slightly different in their inputs.

The Mariners' farm system received a pitch-weighted Stuff+ of 99.5, placing them at the very bottom of the list. In this case, weighting was done purely on innings pitched, so pitchers with a heavier workload contributed more to the metric than those who didn't see as much time on the mound.

At first, this ranking may seem peculiar, especially when considering the likes of Kade Anderson and Ryan Sloan who are respectively ranked the No. 5 and No. 11 prospects in baseball. Yet upon further inspection, it starts to make a little more sense.

"Stuff" has always been an intentionally nebulous term. Before the world of high-tech analytics took over, it was used to describe a certain je ne sais quoi about pitching. Now, scouts can actually describe what goes into assessing it. As with every aspect of player evaluation, different organizations emphasize different things, so it's impossible to know exactly what Baseball America thinks are the biggest weaknesses. But one can sort of infer where they're coming from.

Take Kade Anderson. His four-seam fastball averages just 93.5 mph with an induced vertical break of 16.1 inches. His velocity is already below league-average and the ride he gets on his fastball could also be considered below average compared to other pitchers with high arm slots. His secondary pitches are OK, but hardly anything to write home about, at least on paper, which is why his strikeout and whiff rates were league-average during his seven big league starts.

But a pitcher like Anderson finds success by limiting walks, getting hitters to chase, sequencing pitches in an effective way, and having the right approach to get outs, none of which are qualities that feed into a Stuff+ calculation. There are plenty of pitchers with low Stuff+ numbers that find success, and there are plenty of pitchers with high Stuff+ numbers who don't.

According to FanGraphs, Eduardo Rodriguez posted a 2.89 ERA and 3.89 FIP across 189.2 innings while having a Stuff+ of just 92, fifth-worst among qualified starters. Meanwhile, Aaron Nola had a Stuff+ of 104, 15th among qualified starters in MLB, while posting a 4.67 ERA with a 4.87 FIP over 175.1 innings.

It's far from the be-all-end-all, and it may not even be what the Mariners are looking at when planning who to call up next. Recently, Seattle has placed more of an emphasis on throwing strikes without worrying too much about lighting up the radar gun or throwing frisbee sliders, as those pitches are often harder to properly command. Baseball America admits as much in their own report.

"As we try to note, Stuff+ does not have a location component. One of the limitations of the metric is that it views a nasty breaking slider that lands a foot outside the zone as the same quality as one that dots a corner...The Mariners have a superior strike percentage, but it comes with significantly less impressive stuff."

J.J. Cooper, Baseball America

The lack of sheer stuff is seemingly a glaring weakness in Seattle's young arms, but it's almost by design. After nearly half a decade of relying on premier pitching talent that was brought up entirely within their organization, the Mariners likely aren't sweating about the results of external metrics. They've got everything all under control, just the way they like it.

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