Using the link you provided, but adjusting the 3 Year Rolling to No, so it's one year data each line, we get the following data:
5 YEARS BEFORE NEW GRASS (The fences were moved in prior to 2013):
2013-
Singles: 18th of 30 teams in MLB
Doubles: 5th
Triples: 25th
HR: 22nd
2014-
Singles: 25th
Doubles: 30th
Triples: 27th
HR: 10th
2015-
Singles: 15th
Doubles: 28th
Triples: 20th
HR: 22nd
2016-
Singles: 25th
Doubles: 20th
Triples: 25th
HR: 8th
2017-
Singles: 19th
Doubles: 26th
Triples: 14th
HR: 21st
Average ranking across the 5 years:
Singles: 20.4
Doubles: 21.8
Triples: 22.2
HR: 16.6
THE 5 YEARS AFTER REPLACING GRASS:
2018-
Singles: 22nd
Doubles: 28th
Triples: 14th
HR: 13th
2019-
Singles: 18th
Doubles: 27th
Triples: 27th
HR: 18th
2020-
Singles: 29th
Doubles: 27th
Triples: 29th
HR: 10th
2021-
Singles: 29th
Doubles: 30th
Triples: 27th
HR: 18th
2022-
Singles: 28th
Doubles: 27th
Triples: 30th
HR: 14th
Average ranking across the 5 years:
Singles: 25.2 (which is down 4.8 spots in this 5 year sample compared to 2013-17)
Doubles: 27.8 (down 6 spots)
Triples: 25.4 (down 3.2 spots)
HR: 14.6 (up 2 spots)
So, for all 10 years it was a park that suppressed
everything more than it did homeruns, but that has kicked into overdrive since the new grass was put in.
I don't think it's necessarily
longer grass. However, if you think of it like walking into a Washington forest compared to a California forest, you're going to be in two different ecosystems. There is a much higher moisture content in the forests of Washington. Correct me if I'm wrong. But same goes for soccer fields, football stadiums, baseball fields.
In a game where the ball rolls/bounces across the surface, the Pacific Northwest provides a unique ballpark experience.
If you roll a ball across a field of grass with a high natural water content in a wet climate and compare that to a ball rolled across a field in a dry area, you're going to get two balls rolling/bouncing at a much different speed, even if the drier lawn is watered regularly.
The heartier ground with the higher moisture content/thicker grass causes the ball to roll/bounce across it slower and slow down faster than it does on the naturally drier ground. Same reason it moves faster on turf than on grass.
The end result is infielders are able to get in front of more ground balls before they make it through a hole in the infield,
and balls that do get hit to the gap in the outfield hit the grass and slow down faster than when they hit off a harder/drier ground like what would be found in California or Arizona, for example. Balls rarely roll to the wall in T-Mobile like they do in other parks, limiting hitters to long singles as the outfielder cuts it off instead of doubles and triples that roll to the wall in other parks.