Ask a dozen baseball fans which stadium they think created the most extreme park effects in 2024, and invariably most or all of them will give you the same answer: Coors Field. Colorado's ballpark is famous for the high altitude that affects how pitches move and the huge outfield that¡¯s impossible for outfielders to cover.

They¡¯d be wrong. Coors Field, according to Statcast¡¯s park factors, boosted offense by 10%. Seattle¡¯s T-Mobile Park, on the other end, suppressed it by 11%. While Seattle doesn¡¯t outdo Denver in most years, it¡¯s often close, and for at least one year, the Pacific Northwest was king.

The most impactful ballfield in 2024, as it turns out, wasn¡¯t a mile high. It was at an elevation of all of 10 feet above sea level.

It also made it difficult for Mariners batters to look good at home, and they mostly didn¡¯t. Seattle hitters at home were 30th in average, 29th in slugging, and 28th in runs scored, all dreadful numbers. Yet on the road, they were 22nd, 15th, and 12th, respectively. If not a great offense, the road Mariners were at least an average one.

That same effect also makes Mariners pitchers look considerably better. Remember when we said that the Mariners offense had the lowest home batting average? The flip side of that is that Seattle pitching allowed the lowest home batting average. In fact, at .205, it was actually the fifth-lowest full-season mark in full-season baseball history. While that¡¯s not unrelated to the Mariners' quality rotation, it¡¯s not just that, either. The Mariners staff had the highest strikeout rate (27.2%) at home, yet it was tied for 20th on the road (21.6%).

While the Mariners were an average run-prevention team on the road ¨C 351, exactly 15th ¨C back in Seattle, they allowed just 256 runs, or barely 72% as many. That total of 256 is the third-lowest total of any team in the last eight seasons.

In the same way Coors Field makes it difficult to evaluate how valuable a Rockies player really is, so does T-Mobile Park, just in the opposite direction. Most parks are within some kind of range of "average." Not in Denver, and not in Seattle, either.

You're thinking about the temperature, and the marine layer, and we'll get to all of that because it matters. Yet, stunningly, none of that appears to be the primary issue here. What¡¯s really plaguing hitters at T-Mobile is the kind of park factor that generally doesn¡¯t get considered when you think about the kinds of things a park can do.

It appears, by the numbers and the statements, to be baseball¡¯s biggest strikeout factory. It creates strikeouts. In the same way that Kansas City¡¯s Kauffman Stadium is a better hitting park than you¡¯d expect, given how hard it is to homer here, simply because batters tend to swing and miss less often there, the hitting issues in Seattle begin even before contact is made ¨C and then continue after that.

Put it this way: Eight Mariners pitchers threw at least 20 innings both home and away, and all eight of them had higher strikeout rates at home ¨C none more an outlier than reliever Andr¨¦s Mu?oz, who had this absolutely hilarious home/road split:

• Home, 2024: 0.28 ERA, 43% K, .080/.155/.120
• Road, 2024: 4.28 ERA, 25% K, .225/.352/.392

It was the third-largest home/road split of any pitcher since World War II.

¡°It's definitely hard to hit here,¡± Mariners utilityman Dylan Moore told MLB.com, and he should know, because in 2024, he was the flip side of Mu?oz.

Last year, Moore struck out 34% of the time at home, yet just 24% of the time on the road; his home OPS (.503) was 337 points lower than his road OPS (.840). Among the thousands and thousands of players who had at least 190 home plate appearances since the Wild Card era began in 1995, Moore¡¯s 2024 showed the third-largest home/road split ¨C and his teammate, J.P. Crawford, was sixth on that list, dropping 282 points of OPS at home.

¡°There's a lot of outfield to cover in the cold and winter months, on both sides, both ends of the season,¡± Moore continued. ¡°It's a little bit harder. There's different factors that go into it, as opposed to other ballparks that maybe don't have those factors. It's only hot maybe a couple months out of the year, but at the end of the day, you probably get a little less bang for your buck, I guess is probably the best way to describe it.¡±

Moore is right that it¡¯s cold there (the average temperature of 62.9 degrees was 30th of 30th ballparks), and comparing the actual wOBA on contact (.340) to the expected wOBA on contact (.367), based on the quality of exit velocity and launch angle hitters made there, the resulting deficit of 27 points was the largest of any venue in the Majors. (Coors, to compare, added 29 points of value.)

The numbers all back Moore up. Last year, hard-hit balls pulled in the air in Seattle carried 5.3 feet less than average, the second-weakest carry of any park ¨C and nearly 24 feet less than the +18.4 feet that Coors Field supplied. According to Weather Applied Metrics data, over the last two seasons, there were 55 non-homers in Seattle that with a high degree of confidence would have gone over the fence in calm conditions, second-most lost dingers to Kansas City's 65.

It was a lesson Cal Raleigh learned last summer, when this rocket to center seemed to die softly into Mickey Moniak¡¯s glove. The wind that day cost it a whopping 28 feet of carry.

Less bang for your buck, indeed.

It¡¯s not a one-year issue, either. T-Mobile¡¯s park factor has been below-average essentially every year of the park. Aside from an odd blip in 2007-08, the strikeout rate has been well above average every season, peaking in 2024. (¡°100,¡± here would be read as ¡°average,¡± so their 122 in 2024 means ¡°22 percent more than average.¡±)

So: What¡¯s really going on here? They¡¯ve already tried moving in the fences. It didn¡¯t really work. Besides, how does a park create strikeouts? Let¡¯s dive through some theories.

It¡¯s the ¡­ batter¡¯s eye?

This is the one that comes up the most, perhaps best vocalised by Teoscar Hern¨¢ndez, a one-year Mariner who struggled badly at home in Seattle in 2023, posting a .643 home OPS that was nearly 200 points lower than his road OPS that year.

¡°For some reason, I couldn¡¯t figure it out,¡± Hern¨¢ndez told the Seattle Times last summer. ¡°I couldn¡¯t feel good at the plate at home. I talk to a lot of players around the league, and they feel the same thing when they go to Seattle and play two or three games over there,¡± Hern¨¢ndez said. ¡°They had the same feeling. So it was not only me.¡±

¡°It was a little crooked,¡± Hern¨¢ndez added. ¡°I didn¡¯t feel really straight with the pitcher, for some reason. I moved everywhere in the batter¡¯s box and tried to fix it, but I couldn¡¯t figure it out.¡±

It¡¯s hardly a new concern. Way back in 2003, Ichiro Suzuki and Mike Cameron asked team execs if anything could be done about the batter's eye, and several changes were in fact made. No less a slugger than Alex Rodriguez once said that the ballpark was ¡°the hardest park in the history of baseball¡± to hit in; in 2000, his only full season calling the park home, his .908 OPS there might sound impressive ¡­ until you realize he posted an 1.135 OPS on the road.

In 2004, the Post-Intelligencer noted that future Hall of Famer Edgar Mart¨ªnez ¡°still isn't happy with the so-called batter's eye hitting backdrop in center field, which he believes needs to be more straight than at its current angle.¡± His home OPS that year? Exactly 100 points lower than his road OPS.

There is some thought that maybe it affects righty pitchers disproportionately, given where they release the ball and the viewpoint, and it¡¯s worth noting that the Mariners built a staff almost entirely out of righties, to an extreme. Last year, just 6% of Mariners pitches came from lefties ¨C which is the lowest any team has had since 2016.

While A¡¯s All-Star Brent Rooker did speak quite positively last year about playing in Seattle, it was more about the atmosphere and personnel than the hitting experience itself, remembering a ball that he¡¯d hit extremely hard in 2023 that died on the warning track. On the other hand, Mike Trout specifically said that ¡°I love hitting here ¡­ I see the ball good,¡± and he¡¯s backed it up, hitting .333/.435/.708 in 407 career plate appearances in Seattle, nearly a full season of work. It¡¯s not impossible, and it doesn¡¯t require Trout-level talent, either. Journeyman outfielder Manuel Margot, for example, has hit .286/.375/.667 in 48 plate appearances there.

But those are outliers, and the overall trends are clear. So, what about it? There¡¯s not really a ranking of batter¡¯s eyes in any real way, though FanGraphs has tried. We can¡¯t tell you for sure if this matters, and how much. But maybe we can at least see if this one is different, in terms of angle and distance.

As it turns out, the angle of Seattle¡¯s batter's eye is indeed rare ¡­ but it¡¯s not unique. Of the 30 parks in use in 2024, we count 24 of them that had batter¡¯s eyes that were perfectly straight (0 degrees left to right) or close enough that it¡¯s not worth parsing. Three had angles where the eye was angled considerably from left field to right, in terms of getting farther away as you go to right field (think Fenway Park) and three, like T-Mobile, had notable getting-farther-toward-left field angles of 12 or more degrees ¨C with Baltimore and Cleveland joining Seattle.

OK, so maybe Cleveland doesn¡¯t quite feel the same, with the trees and greenery and closer eye than the other two. But Baltimore¡¯s eye is on a slightly sharper angle than Seattle¡¯s, and it¡¯s farther from the fence, too ¨C though Seattle¡¯s does extend farther toward left field. Both T-Mobile and Camden Yards face the same direction as well, each roughly average among Major League parks. So it might be this, given all the talk from hitters, but it¡¯s hard to explain why none of the same issues are present in Baltimore, too.

You can take this either as ¡°plausible, since players keep talking about it and only one other park is really like this¡± or ¡°overrated, since there is another park like this that doesn¡¯t have the same issues.¡±

Maybe, though, it¡¯s not just the angle. It¡¯s what the angle does.

It¡¯s the ¡­ sun?

In 2003, an Associated Press article referenced ¡°the ballpark's notorious evening glare¡± and the team¡¯s attempts to combat it. Before the 2002 season, they¡¯d planted trees in front of the batter¡¯s eye, likely in part because of what infielder Bret Boone had said to local media.

¡°We can see fine,¡± Boone said. ¡°The only time we can't see is during those 4 o'clock starts on a sunny day when they refuse to close the roof.¡± That may have been so, yet Boone, surprisingly, had posted no home/road or day/night splits at all the previous year, his first as a Mariner. As for the trees, they didn¡¯t even last a full season; the team removed them in August, 2002, with a team exec saying ¡°most of our hitters wanted them removed.¡±

Boone, weeks before, had said ¡°it's a bad feeling to wake up in the morning and think, 'We have a 6 p.m. game, oh, great,'¡± a feeling echoed by catcher (and now manager) Dan Wilson, who had said that the early evening light ¡°can be so brilliant it is blinding ¡­ it's hard to pick up velocity and spin.¡±

One analyst, Ryan Blake, dug into the idea recently, looking specifically into time of day and the position of the sun, going far deeper into changing aspects of altitude and azimuth than we¡¯re going to do here. ¡°Performance literally changes with the sun in Seattle,¡± he wrote, pointing out that ¡°the sun is, definitively, a predictor of performance in Seattle.¡±

Blake ¨C and Boone, and Wilson, decades before ¨C might be onto something, given what president of baseball operations Jerry Dipoto said to MLB.com at the Winter Meetings in December.

¡°I don't think it's an everyday thing,¡± Dipoto said. ¡°It's an occasional thing based on the position of the sun at a given time for a short period of time during a game.¡±

Does the data back it up? Maybe. We looked at Mariners hitters over the last four seasons at home, excluding cloudy and overcast days ¨C going for the clear and mostly sunny days that Boone was referring to ¨C and looked at what time of day the highest whiff rates were seen. Wouldn¡¯t you know it: The only three hours, on those non-overcast days, where it got above 30% were 4 p.m., 5 p.m., and 6 p.m.. The only times where the sunny/clear whiff rate was more than 1 point higher than the overall whiff rate were in the 5 p.m. and 6 p.m. hours.

The ¡°maybe¡± there is that this might change over the many months of the year as the sun is in different points in the sky at different times, and we haven¡¯t dug that far into it ¨C plus the pattern wasn¡¯t exactly the same for the pitchers. But: maybe.

¡°The issue,¡± Dipoto told MLB.com, ¡°just might be the angle of the ballpark, and I don't think you can reconstruct the ballpark, so it would be a challenging thing to do.¡±

It¡¯s the ¡­ wind! But not the wind you think it is.

When you hear about wind affecting a baseball game, you¡¯re usually thinking of the gusts that, depending on the time of year, can make a place like Wrigley Field play like two completely different parks. When we looked into the famous Ted Williams ¡°red seat¡± in Boston, we determined that his home run was probably more like 525-530 feet, in part because there were gale-force winds in the area that day. As we said above: the ball really doesn¡¯t carry well at T-Mobile Park. That¡¯s known. But that¡¯s only a factor if you hit it.

Yet there¡¯s another kind of wind you don¡¯t really think about, and that¡¯s the wind between the mound and the plate. There was compelling evidence that the wind in Citi Field last October gave Walker Buehler¡¯s breaking balls more movement in the NLCS, as he threw his four biggest-breaking pitches ever. There¡¯s also strong evidence that Kerry Wood¡¯s 20-strikeout game in 1998, usually in the conversation for The Greatest Game Ever Pitched, came with the benefit of winds that began to gust pretty much right after the game¡¯s 1:20 p.m. local start. Just look at what wind did to this Noah Syndergaard pitch years ago.

Thanks to the partnership with Weather Applied Metrics, Statcast has over the last two seasons been better able to measure the effects of wind in each park. While Seattle isn¡¯t the windiest park overall, would you be surprised to learn that it¡¯s tied with another notorious pitcher¡¯s park, San Francisco¡¯s Oracle Park, for the most tailwind? To imagine what that means in practice, just think about how much faster you can fly cross-country from west-to-east, with the wind at your back, as compared to east-to-west, into the wind. Moving air can affect a plane, and it can affect a baseball.

What does that mean in practice?

¡°Tailwind is good for fastballs, bad for breaking balls,¡± said MLB.com data scientist Clay Nunnally. ¡°This chart is basically showing how efficient a park is at turning wind into tailwind, and Seattle is an outlier in this respect. Compared to San Francisco, for example, Seattle needs less forcing function (prevailing wind) to generate the same amount of tailwind on pitches.¡±

Good for fastballs? It¡¯s worth noting that on fastballs, Mariners pitchers had a considerably higher swing-and-miss rate at home (25%) than on the road (20%) ¨C and Mariners batters had the exact same thing happen*,* 25% whiff at home and 20% on the road. We¡¯d say that seems like a significant factor that¡¯s worthy of further investigation.

It¡¯s probably not the roof.

Although the hitters definitely have a strong preference.

Remember, first, that T-Mobile¡¯s roof being closed doesn¡¯t really make it a domed stadium, like happens in Toronto when the Blue Jays close their roof. Instead, it¡¯s more of a covering to protect against precipitation. Outside air can still enter, and the temperature doesn¡¯t change much. ("It's a big umbrella on wheels," Mariners groundskeeper Tim Wilson said in 2021.)

"I think we did it more last year, close the roof, like when it was particularly cold or windy than we've done in the previous seven years that I had been here,¡± said Mariners general manager Justin Hollander in December. ¡°We just made a decision based on the comfort of players and fans, to close the roof and try and tamp down the wind a little bit.¡±

The data doesn¡¯t totally support that ¨C the roof was closed as often as it was the previous two seasons ¨C though Hollander is clearly correct that it¡¯s been closed more the last three years than in the previous three full seasons.

Percent of games with roof closed in Seattle

• 2024 // 16%
• 2023 // 16%
• 2022 // 16%
• 2021 // 11%
• 2019 // 4%
• 2018 // 8%

But it might not have mattered much. Over the last three years, the park suppressed offense by 9% with the roof closed, and 9% with the roof open. Over the same span, their hitters at home struck out 26% and slugged .383 with the roof open, and 27% and .355 with the roof closed. As we said, the canopy-type roof means that it stays cold even if it¡¯s closed. This might not be it.

What does it all mean?

If the park isn¡¯t going to change ¨C or if changes haven¡¯t helped ¨C maybe the approach can. It wasn¡¯t a big sample, but it was worth nothing what happened at the end of the season. In late August, the Mariners made a number of coaching changes, including returning franchise legend Martinez to the hitting coach role he¡¯d held from 2015-18. The September Mariners had by far their best month of the season, particularly at home, cutting their strikeout rate from August¡¯s 30% to 23%, and posting a .774 OPS ¨C their best month at home in more than a year.

Maybe it¡¯s a small sample fluke ¨C we¡¯re looking at half of one month. The roster had changed too, as veterans Justin Turner, Randy Arozarena, and Victor Robles had been acquired in-season, while star Julio Rodr¨ªguez had shaken off his usual cool start to finish strong. On the other hand, hitters raved about Martinez¡¯s ¡°liners up the middle approach,¡± and he¡¯ll direct the team¡¯s hitting program in 2025 with Kevin Seitzer as the new daily coach.

¡°Our ballpark might not be conducive to doing it quite the way we have (in the past),¡± Dipoto said in late September. ¡°Shame on us for taking this long to understand that.¡±

¡°It's just adapting a team to the ballpark,¡± Dipoto told MLB.com in December. ¡°It's not trying to adapt the ballpark to some fictional team."

Perhaps so ¨C though the underlying data about pull rate and grounders wasn¡¯t meaningfully different, not moreso than simply the roster changes. (Although it¡¯s worth pointing out that Raleigh really did have a massive strikeout drop, from 33% in the first half to 22% in the second.) File the September Mariners improvement under "intriguing, not yet convincing."

Either way, this isn¡¯t a new issue. It¡¯s not one the team has ignored, or not tried to fix. It¡¯s incredibly difficult to hit at T-Mobile. It always has been. It's a bigger factor than most people consider ¨C and it¡¯s important to keep that in mind when you¡¯re worried about whether or not Mariners hitters are successful.

MLB.com¡¯s Daniel Kramer contributed to the reporting of this article. MLB.com data scientist Clay Nunnally supplied tailwind research. MLB.com's Jason Bernard assisted with hour-by-hour research.