Why playing at T-Mobile Park should be an advantage (and not a weakness) for Mariners

One of the biggest complaints of Seattle Mariners fans in recent years has been about the performance of the team's offense, particularly at home. While it is true that the Mariners offense has not been great, the unit isn't necessarily struggling because of the quality of the players. Rather, the ballpark is the most difficult to hit at in all of baseball. It has always been hard to produce runs in Seattle, but now we know just how hard it is, and it should be viewed as a strength, not a weakness.

Recently, Mike Petriello of MLB.com did some great research about T-Mobile Park and compared it to the rest of the league. He found that in 2024 it was the most extreme ballpark in all of Major League Baseball when it comes to either enhancing or suppressing offense. Coors Field in Colorado has been known as one of the best hitting environments in baseball, but last year T-Mobile Park was a notch more extreme in terms of suppressing offense than Coors was at improving offense.

For years, the Colorado Rockies have really struggled to find any consistent quality starting pitchers because for 81 games a year they play at Coors Field. That environment turns good pitchers into average to below average pitchers. Since the Rockies hitters benefit from playing those same 81 games a year there, the ballpark turns average hitters into good or even great hitters when they are at home.

The Mariners have the opposite happen in Seattle, and the front office may have been building their team to fit their ballpark, something that President of Baseball Operations Jerry Dipoto talked about early on in his tenure with Seattle. The Mariners' strong rotation is among the best in the league and would find success anywhere, but would the same five starters that pitched for Seattle in 2024 have been as elite if they played half their games in Coors Field instead of T-Mobile Park? That would be highly unlikely.

In the article by Petriello, he highlighted Mariners electric closer Andres Muñoz's stats last year at home and on the road. At home, Muñoz had a 0.28 ERA with a strikeout percentage of over 40%. Opposing hitters owned a sub-.100 average against him. On the road, his 4.28 ERA, 25% strikeout rate, and .225 batting average against were considerably worse. That is a huge swing. Muñoz went from putting up prime Mariano Rivera numbers at home to being a bad reliever on the road.

Petriello also noted that the large disparity in home/road splits for Muñoz was the third-largest since World War II. Those are dramatic numbers and show just how much the ballpark helps the Mariners pitchers. George Kirby, Logan Gilbert, Bryan Woo, Luis Castillo, and Bryce Miller would all still be solid big league starting pitchers in an average ballpark environment, but they might not be as highly praised if they did not pitch in T-Mobile Park for half of their starts.

Below is a chart of the Mariners' five starting pitchers career ERA numbers at home compared to on the road. Obviously there is more that goes into pitching and using ERA as a metric, but this is a good measure that shows how every single one of them benefits to different degrees at T-Mobile Park. Also, Luis Castillo is the only one to have ever pitched at a home ballpark besides T-Mobile Park, since he started his career with the Cincinnati Reds.

To show an example of how much the Mariners hitters were impacted by the ballpark as well, Petriello showed that Dylan Moore's OPS was .503 at home, which is not a good number, and .840 on the road, which is an All Star-level mark. His strikeout rate was also 10% higher at home than it was on the road. Now, Moore is not an All Star level player, but if he played in Colorado instead of Seattle, would his career look more like former Rockies infielder DJ LeMahieu?

However, just because it is hard to hit in Seattle does not mean that anything is wrong with the ballpark, or that the fences need to be moved in, or that the batters eye needs to be repainted or shifted. The Mariners have a tremendous advantage on the mound at home and that should be viewed as a strength.

It might not be worth it for Seattle to make a change to the ballpark to get more offense because if the run scoring gets marginally better it could very easily make the pitching much worse. The Mariners simply have a ballpark that favors pitchers more than any other, so they should continue to focus on getting good pitchers to amplify that strength.

Obviously this does not mean that the Mariners will never be able to have a good offense. It might just mean that they have to target certain types of players or go after those that are good enough to not have their numbers fall off a cliff at T-Mobile Park.

We saw the Kansas City Royals build multiple World Series teams around pitching, speed, and defense, and the Mariners could benefit from doing the same.