Why Mexico City Series Might be Big Trouble for Zac Gallen

These are not the most favorable conditions.

Apr 12, 2026; Philadelphia, Pennsylvania, USA; Arizona Diamondbacks starting pitcher Zac Gallen (23) looks on after leaving the game against the Philadelphia Phillies in the sixth inning at Citizens Bank Park. Mandatory Credit: Kyle Ross-Imagn Images | Kyle Ross-Imagn Images

Arizona Diamondbacks right-hander Zac Gallen has been getting away with hard contact all season. He might not be able to on Saturday afternoon.

The Diamondbacks head south to Mexico City this weekend for a two-game series against the San Diego Padres. But alongside the excitement of an international showcase comes a unique, challenging condition: the severe elevation of Mexico City.

And that elevation could spell danger for Gallen against a hot-hitting Padres club.

Diamondbacks' Zac Gallen may run into trouble in Mexico City Series

Apr 1, 2026; Phoenix, Arizona, USA; Arizona Diamondbacks pitcher Zac Gallen in the second inning against the Detroit Tigers at Chase Field. Mandatory Credit: Mark J. Rebilas-Imagn Images | Mark J. Rebilas-Imagn Images

Mexico City sits at an elevation of over 7,300 feet. Many might compare this environment to that of Coors Field Denver, Colorado — except over 2,000 feet higher.

Simply put, the baseball is going to be jumping off the bat this weekend, and likely sailing quite far. Farther, perhaps, than Gallen will be able to afford.

It's not a secret that Gallen is no longer the heavy swing-and-miss pitcher he once was. The right-hander has recorded only 14 strikeouts over his first 25.2 innings of the 2026 season, with a career-worst whiff rate of 16.2%.

He's also giving up the hardest contact of his career. Gallen's hard-hit rate is 47.2%, with an average exit velocity of 92.2 MPH — a bottom-10% figure, per Statcast.

And while Gallen's ERA is a sturdy 3.51, his expected ERA (xERA) is 5.33 — a number that takes into account quality of contact and exit velocity.

So while Gallen has only given up two home runs thus far in his five starts, the thin Mexico City air could greatly exaggerate fly ball events against the D-backs right-hander.

Ground balls and swing-and-miss will be key to any pitcher in this series. Gallen has maintained his slightly-above-average ground ball rate (46.6%), but will face somewhat of a pitcher's dilemma on Saturday afternoon.

He'll need to keep the ball out of favorable hitting spots for San Diego's sluggers, while still avoiding walks as much as possible. If he does stay out of the zone, the extra runners could bite the D-backs, while living in-zone could result in further-traveling fly balls and a home run derby.

This series' conditions certainly won't be a stress-free one for any of Arizona's hurlers, except, perhaps, the ground-ball-heavy Ryan Thompson.

Regardless, the Padres are a red-hot club. Even outside of the external conditions, the Diamondbacks are about to have their hands full for the next two games.

Coming off a tough series loss to the Chicago White Sox, Arizona won't get a chance at another losing-record club until, potentially, May 8 against the struggling New York Mets