John Mozeliak's old mantra is particularly applicable to this young Cardinals bullpen arm

The gap between Triple-A and the major leagues has seemingly grown wider with each passing season. Every year, you hear about players who are dicing up the minor leagues only for them to receive a long-awaited promotion and fall flat on their face. In that sense, Luis Gastélum's brutal introduction to the major leagues shouldn't come as a massive surprise. But as St. Louis Cardinals fans call for the skull of the 24-year-old changeup artist, Gastélum's bullpen role means he warrants an especially long leash.

Most pitching prospects come up through their team's farm system as starters. Some continue on that path in the major leagues, and others receive the boot to the bullpen. Players of Gastélum's ilk are less common on teams' top-prospect lists: those who received the reliever label early but are so dominant in that role that they thrust their way onto scouts' and fans' radars anyway.

Gastélum befuddled batters in the minor leagues with his devastating changeup, but the sledding has been far tougher against big-league batters. He has allowed 12 runs on 16 hits in 13.1 innings with the Cardinals since his promotion in early July, and fans are already proclaiming him to be a failure.

But while Gastélum has so far failed to confound major league hitters with his off-speed pitches, his position necessitates more chances than starting pitchers generally receive. If a starting pitcher doesn't perform well in one inning, he will often still get the ball for a few more innings after that for a chance to get on track. Relief pitchers don't have that luxury: For most relievers, it's approximately one inning per outing, meaning there's less for coaches to go off of when helping the player identify flaws and develop his game.

The nature of relief pitching means that manager Oli Marmol will need to continue throwing Gastélum into games so he can keep getting reps to improve. And while fans may decry Marmol for continuing to go to Gastélum in situations where a more established pitcher may be the better option, it's difficult for one to improve his game at the highest level while riding the pine.

And let's not kid ourselves: The Cardinals aren't going to be serious postseason players in 2026. This was a "runway" season for young players to show whether they can be a part of the next competitive Cardinals team, and it's far too early to judge Gastélum to be someone on the outside looking in.

Gastélum still has every chance to be a menace in the Cardinals bullpen

Gastélum's time in the majors so far may not be anything to write home about, but the right-hander still holds plenty of upside. His Statcast metrics and FIP suggest there is some misfortune in play here, and opponents' low exit velocity and hard-hit percentage are encouraging signs for his future.

Velocity is king in today's iteration of baseball, especially out of the bullpen, making Gastélum's 94 mph fastball seem like a novelty. But his changeup, which MLB Pipeline rates as a 70 on the 20-80 scale, can provide batters a different look from the scorching heat they've come to expect, and some fine-tuning of that cambio may be all Gastélum needs to get everything humming at the highest level.

In a worst-case scenario, Gastélum continues to tantalize with his outlandish changeup but never finds a method to make it effective against major league hitters. This could lead to a career similar to that of Chris Roycroft, a former Cardinals reliever who had exceptional extension and ridiculous arm-side run on his sinker but couldn't find success with St. Louis.

A higher-end projection for Gastélum could be Tommy Kahnle, a fellow off-speed aficionado who has put together a highly respectable career. There is a wide range of outcomes here, and although Gastélum's major league performance hasn't been pretty to this point, the Cardinals should continue to trot him out frequently for the remainder of the season. Fans don't want to hear it, but it's time to be patient as the Cardinals work on identifying what Gastélum can ultimately become.

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