SEATTLE — The Seattle Mariners’ home, T-Mobile Park, opened July 15, 1999, as the crown jewel of the Sodo District. On vintage Seattle summer days, you won’t find a better environment anywhere in America to take in a ballgame. The scene can be truly stunning — baseball paradise for some — and that remains as true as ever as the stadium nears its 25th anniversary.
What also remains true: The place can be a hellhole for hitters.
No ballpark in Major League Baseball suppresses offense as much as T-Mobile Park. Players bemoaned that in its early days, and new technology over the past decade has validated that reputation.
Call it a pitcher-esque park.
What’s more: Through the first month of this season, offensive output in Seattle has reached a new low, with run production values at T-Mobile Park ranking dead last among all MLB venues.
There are many factors at play.
On-field talent is one, certainly. The scarcity of runs in Seattle over the past few years, in particular, has coincided with the rise of the Mariners pitching staff as one of the best in baseball, capable of shutting down any opposing lineup.
Environmental effects are factors too, of course. Climate, humidity and wind play a part in any park, and T-Mobile Park has one weather phenomenon — the dreaded marine layer — that has become as notorious as the boogeyman for some hitters.
What is the marine layer? When does it emerge? What effect does it have on the flight of a baseball? And, maybe as important as anything, what effect can it have on the psyche of a big-league hitter?
Let’s turn to an expert.
Layer up
Yes, Cliff Mass said, the marine layer is real. Yes, it can be something of a kryptonite to baseball’s super sluggers.
Mass is a meteorologist and professor of Atmospheric Sciences at the University of Washington, and he said the low elevation here has as much of an environmental effect as anything on the flight of a baseball.
“You have to start with this fact: We’re near sea level, and that means the air is dense and that means the baseballs don’t go as far,” Mass said.
The marine layer is a shallow layer of air that forms when warm air moves atop a body of cooler water and becomes saturated with water vapor. It’s more than just fog or thick clouds, and it’s typically strongest in cooler temperatures in the spring.
Through the first month of the season, the average temperature for the start of a Mariners game has been 53.3 degrees (don’t forget your winter coats, kids). That’s the third-coldest average among all major-league parks, according to MLB’s Statcast metrics; only games at Pittsburgh’s PNC Park and Chicago’s Wrigley Field have been colder.
Cold air is more dense than warm air and, as Mass explained, higher air density creates more drag force on a ball in flight.
“We know the environment here. We’re in a relatively cool spot and the marine layer dominates most of the time,” Mass said.
So just how much is the marine layer to blame for Seattle’s run suppression?
In a research paper published in The Hardball Times in 2017, authors David Kagan and Chris Mitchell studied the effects of the marine layer at MLB’s six West Coast venues (Seattle, Oakland, San Francisco, Los Angeles, Anaheim and San Diego).
Their conclusion: 6 feet.
The marine layer, on average, reduces the distance of fly balls by about 6 feet in those parks, their study found.
As the authors noted, there are many variables to account for — within weather patterns in various locations and within an individual baseball game — and the analysis isn’t foolproof. But they did find consistent data that the “marine layer has a statistically significant effect on fly-ball distance … [and] that almost certainly isn’t a fluke.”
Those 6 feet can turn a potential game-changing home run into a harmless warning-track fly out, and any Mariners hitter who has played long enough inside T-Mobile Park probably can think of at least one time when they thought they’d mashed a towering homer — only to jog back to the dugout dejected.
And yet, those 6 feet aren’t overwhelming enough to alter the course of a typical game. The physical effect of the marine layer, the authors concluded, is minimal.
Which leads to another hypothesis:
“Could the effect,” they wrote, “be as much psychological for hitters that as much as it a scientific phenomenon?”
‘It’s a mental battle’
You want to get inside a hitter’s head? Now that’s a layered discussion.
Alex Rodriguez, before signing his mega free-agent contract and moving to the cozier warmth of Texas late in 2000, played his final year and a half with the Mariners at then-Safeco Field. Rodriguez openly (and, often, loudly) campaigned for the retractable roof to be closed, convinced fly balls carried better with cover. To this day, Mariners hitters continue to plead for the roof to be closed on cooler days.
By 2012, the organization put together a small committee to study the ballpark’s effects on the depressed offense. The committee concluded that the fences needed to be moved in, and the new dimensions were constructed (with the fence moved in up to 17 feet in left field) for the start of the 2013 season.
“Ultimately, that’s what gets to hitters,” Jeff Kingston, the assistant general manager at the time, said then. “If they square a ball up and don’t get rewarded, they start to change their swing and it wears on them mentally.”
The dynamics of the sport have changed dramatically over the past decade. It’s a pitcher’s game now. They are throwing the baseball harder than ever, spinning it more than ever, and it’s generally accepted that pitching is more dominant than it’s ever been.
In 1999, the leaguewide batting average was .271 and hitters struck out in 16.4% of their plate appearances.
In 2024, the leaguewide batting average is .239 and hitters are striking out in 22.5% of their plate appearances.
It’s harder than ever to hit a baseball. Add in the inherent challenges of trying to hit outdoors in Seattle — and, naturally, some have not handled it well.
Jesse Winker was billed as the Mariners’ biggest offensive addition in 2022. Winker had played previously in the hitters’ haven of Cincinnati, and the drop-off in Seattle was glaring: He hit just .203 with a .625 OPS at T-Mobile Park that season.
Teoscar Hernandez was billed as the Mariners’ biggest offensive addition in 2023. Hernandez had spent the bulk of his career hitting in Toronto’s indoor stadium, and he later acknowledged he was never comfortable hitting at T-Mobile Park. His production last year said as much; he had an .643 OPS in Seattle and a .830 OPS on the road.
Winker and Hernandez are hardly the only hitters to struggle to make transition in Seattle.
Mitch Haniger had to learn how to hit in new home park when he arrived in Seattle in 2017. Seven years later — after a one-year hiatus last year in San Francisco, another daunting park for hitters — Haniger has hit 54 home runs at T-Mobile Park, tied with Edgar Martinez and Ichiro for the eighth-most at the venue. (Kyle Seager ranks No. 1 with 94 homers at T-Mobile Park.)
“It’s a mental battle that some guys have to face and conquer here,” Haniger said. “There’s some guys where it really does affect them. I think you have to buy into not caring [where you are]; if you’re attaching yourself to the results so much, you’re going to cause problems [for yourself].”
New approach
The elite pitching, the cold weather, the marine layer air — they’re all conspiring against big-league hitters in Seattle.
And instead of pretending none of those things matter — or that they don’t exist — Scott Servais took a new tack with his hitters coming into this season. He wanted to address the elephant in the room, as he called it.
“It’s the reality,” the Mariners manager said, “so you might as well talk about it. … We’ve seen players overthink it, and I just thought we’d be better off trying to get ahead of it.”
None of that is intended to serve as an excuse for the Mariners’ offensive issues through the first month of the season.
Mariners hitters had a .204 batting average, a .624 OPS and a 30.2% strikeout rate in their first 19 games at T-Mobile Park, compared to a .239 average, a .686 OPS and a 26.5% strikeout rate through their first 12 road games.
The Mariners entered the week atop the AL West, and Servais remains steadfast that the offensive production will improve, as it historically does when warmer temperatures arrive in the summer.
The flip side, of course, is Mariners pitchers have benefited from the conditions in their home park — this has a chance to be the best staff in franchise history — and the club has tried to strategically construct a roster that suits its ballpark.
Servais said he is hearing less grumbling about the ballpark conditions from hitters in the dugout early this season.
“Our guys have done a better job of not letting it distract them,” he said. “It is what it is, you know. Just hit the ball on a line and try to keep the ball out of the air at certain times. You can still hit home runs here, but you’ve really got to hit it.”
The best approach to hit through the marine layer?
Don’t hit into it.
Haniger has always seen himself as a line-drive hitter; he’s simply trying to hit the ball hard into one of the gaps — not up in that dense air.
“I love it here. I’m comfortable here,” Haniger said. “I think the more you can just measure success on like the stuff you can control the better off you’ll be.”
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