The Seattle Mariners have been one of the most perplexing teams in all of Major League Baseball this season. Currently leading the American League West with a 38-30 record, the Mariners have achieved this early season success by pairing one of the league’s best pitching staffs (3.60 SIERA and 16.9% K-BB) with one of the most disappointing offenses (.298 wOBA) in all of baseball. In an attempt to improve their team’s offensive performance moving forward, Seattle dismissed their bench coach and offensive coordinator Brant Brown on May 31st.
Since its opening, T-Mobile Park has been known primarily as a pitcher’s park due to its large outfield dimensions as well as the cold and wet climate of the Pacific Northwest, which suppresses fly balls. With the Mariners having difficulty acquiring productive offensive players in recent seasons (such as Jesse Winker, Eugenio Suárez, Teoscar Hernández, and Kolten Wong), it can be speculated that these park factors are holding back the offensive potential of the Mariners.
On the other hand, it can be argued that T-Mobile Park has contributed to the success of Seatle’s standout pitching rotation. This article will break down how the park factors of T-Mobile Park affect certain players, identify the cause of these phenomena, and attempt to determine whether T-Mobile Park helps or hurts the Seattle Mariners.
Statcast Park Factors
First, a quick primer on park factors. One of the many elements that make baseball unique amongst the four major professional sports is that every ballpark has different dimensions. Ballparks with shorter fences, such as Great American Ball Park, are considered hitter-friendly while ballparks with deeper fences such as Oracle Park and Citi Field are considered pitcher-friendly. Park factors can be explained by more than just outfield dimensions. Factors such as altitude, wind patterns, and surrounding buildings can all play a factor in determining whether a particular ballpark is hitter or pitcher-friendly.
Baseball Savant calculates park factors for each major league ballpark using Statcast data and measures them using a three-year rolling average to reduce year-to-year variance. Statcast Park Factors are scaled so that 100 is a neutral ballpark and each 1 point above or below 100 is equal to 1% above or below league average (ex. a park factor of 95 would benefit pitchers by 5% above average).
Taking a look at the three-year rolling park factors, T-Mobile Park has been the most pitcher-friendly ballpark in all of Major League Baseball with a park factor of 92 since the start of the 2022 season.
In addition to overall park factors, Statcast calculates park factors for various statistics such as wOBAcon, hits, home runs, walks, and strikeouts. T-Mobile Park is overall a difficult ballpark for hitters to hit, as the park ranks well below average in runs, hits, and home runs. While the large outfield dimensions certainly play a role in limiting home runs, it can be assumed that the cold and wet climate of the Pacific Northwest also plays a role in suppressing fly balls.
One standout aspect of T-Mobile Park’s park factors is the large amounts of strikeouts the ballpark induces with a strikeout park factor of 113, ranking as the most strikeout-friendly park in all of Major League Baseball.
As shown by the table above, the five most strikeout-friendly ballparks in all of Major League Baseball are T-Mobile Park, American Family Field, Target Field, Truist Park, and Tropicana Field.
Are there any similarities between these five parks that can explain why they increase strikeouts? Truist Park and Target Field are both open-air stadiums that are located on opposite sides of the country, which doesn’t result in many similarities. On the other hand, Tropicana Field is a dome and American Family Field and T-Mobile Park are retractable roof stadiums which could indicate that these are controlled environments that allow for pitches to perform at their maximum effectiveness.
To analyze this effect, I used my pitch quality model (which does not adjust for environmental effects) in order to see if a pitcher’s “stuff” happens to play up at any of these ballparks.
As shown by the table above (with 100 aStuff+ being league average), pitches do appear to play up at Tropicana Field so we can conclusively say that domed stadiums provide an advantage to pitchers, however, since Tropicana Field is the only fixed dome stadium remaining in all of Major League Baseball, it appears that this phenomenon only applies to this stadium. Pitch quality at T-Mobile Park remains around league average which indicates that other factors besides environmental factors play a role in the increased strikeout environment at the park.
Pitch-by-Pitch Breakdown
To obtain a better understanding as to why the strikeout environment is elevated in Seattle, it makes sense to analyze the whiff rates for each pitch type at T-Mobile Park. To complete this analysis, I queried all pitches grouped by pitch type from the 2022 and 2023 seasons and compared their whiff rates when utilized at T-Mobile Park versus all other major league ballparks.
As shown by the table above, four-seam fastballs generate considerably more whiffs at T-Mobile Park (25.1% Whiff) than they do at all other parks (21.9% Whiff). Splitters, sweepers, sinkers, and sliders also generate more whiffs in Seattle than they do at other ballparks across the league. This is certainly a fascinating development, and I am curious as to why this might be the case.
Given the minimal difference in average pitch quality compared to the rest of the league, it appears unlikely that environmental and climate effects are the primary reason why these pitches generate more whiffs in Seattle than other ballparks, and I wonder if the batter’s eye is a primary contributor to the park’s increased strikeout environment.
Associated Press/Joe Nicholson
As shown by the image above, T-Mobile Park has a batter’s eye that is slanted diagonally relative to home plate as opposed to the parallel alignment present in many ballparks. It is presumably slanted in this alignment to accommodate the bleacher section that is located underneath the center field scoreboard. I hypothesize that this batter’s eye alignment creates perception issues for hitters, as hitters are not accustomed to hitting against a backdrop that is aligned in such a fashion. Similar to how deception in a pitcher’s delivery can baffle hitters and minimize their production, a deceptive batter’s eye can also give opposing hitters difficulty in the batter’s box.
Effects on Mariners Pitchers
Given the increased strikeout environment at T-Mobile Park, it would be reasonable to expect that the Mariners’ pitching staff would perform better at home than on the road. As explained in the last section, four-seam fastballs see the largest increase in whiff rate in Seattle relative to the rest of the league, so it makes intuitive sense to analyze how effective the four-seam fastballs of the Mariners’ starting rotation were at home versus on the road last season.
As shown by the table above, George Kirby, Luis Castillo, and Bryce Miller have seen significant increases in their four-seam fastball whiff rates when playing at home, while Bryan Woo and Logan Gilbert have experienced a more minimal impact.
On a micro level, this provides some anecdotal evidence that four-seam fastballs do indeed generate more swing-and-miss at T-Mobile Park as these pitchers do not make any meaningful shape differences to their four-seam fastballs when pitching at home versus on the road. To evaluate these effects on a macro level, it makes sense to analyze the difference in strikeout rates that these pitchers produced last season at home compared to on the road.
As shown by the table above, Bryan Woo, Luis Castillo, and George Kirby experienced the biggest strikeout improvement at home, while Logan Gilbert and Bryce Miller had minimal differences in strikeout rates when pitching at T-Mobile Park. Included in this table are the horizontal release points and horizontal release angles of each pitcher’s four-seam fastball. While I am limited in regards to the amount of time I have to research if this relationship exists statistically, it anecdotally appears that there is a relationship between lower release height and larger horizontal release angle with an increased strikeout rate at home.
This appears to be backed up by the Mariners’ organizational philosophy of developing pitchers with lower release heights in their minor league system. While this is a general oversimplification of the effects release height has on pitch effectiveness, I wonder if pitches at certain release heights interact with the T-Mobile Park batter’s eye in such a way that causes increased deception to a hitter’s perception at the plate. Either way, the increased strikeout environment at T-Mobile Park has aided in the development of the Seattle Mariners‘ pitching staff, resulting in Seattle having one of the best starting rotations in all of Major League Baseball.
Effects on Mariners Hitters
While the increased strikeout environment at T-Mobile Park has resulted in the Mariners boasting one of the best pitching staffs in the entire league, this environment has given Seattle a lot of difficulty in acquiring hitters over the past couple of seasons. As mentioned earlier, the Mariners currently lead the American League West by pairing one of the best pitching staffs with one of the most disappointing offenses in all of baseball. This phenomenon did not begin this season, in fact, it has been occurring over the past three seasons.
While Seattle’s offensive production has decreased as a whole this season, the Mariners have produced a higher wOBA on the road than at home in each of the past three seasons. As the saying goes, “There are pros and cons to everything”, and the downside of playing at a ballpark that elevates the performance of the pitching staff is that it is going to suppress the offensive production of the starting lineup.
While the Mariners have made several attempts over the past couple of offseasons to upgrade their starting lineup, the team has experienced mixed results in their efforts to acquire impact bats. Circling back to the discussion on how whiff rates on four-seam fastballs increase at T-Mobile Park, let’s take a look at how a few notable acquisitions fared at hitting four-seam fastballs in Seattle.
As shown by the table above, most of the Mariners’ prominent offensive acquisitions over the past few seasons have experienced elevated swing-and-miss on four-seam fastballs when playing at T-Mobile Park compared to other ballparks. Jesse Winker, Eugenio Suárez, and Teoscar Hernández experienced elevated whiff rates at home during their first seasons in Seattle, while Adam Frazier and Kolten Wong saw their splits remain relatively constant. Still only two months into his tenure as a Mariner, Mitch Garver has a 4.3% higher whiff rate on four-seam fastballs at home so far this season.
At a glance, it appears that players who make a lot of contact on four-seam fastballs have a better time adjusting to the elevated strikeout environment in Seattle, as Adam Frazier was able to maintain his overall level of production during his full 2022 season with the Mariners. While Kolten Wong was able to make more contact against four-seam fastballs at home than on the road in his only season as a Mariner, most of his decline in offensive production in 2023 can be attributed to his regression in batted ball quality.
How should this phenomenon affect how the Mariners acquire hitters moving forward? One conclusion to draw is that hitters with high whiff rates against four-seam fastballs will likely not adapt well to hitting at T-Mobile Park. This means that it is a safer bet for Seattle to acquire a hitter closer to Adam Frazier than Teoscar Hernández if they want to improve their offensive production at home. Perhaps it could be a sound strategy to acquire power bats to slug their way to victories on the road while trusting that the pitching staff will be able to take advantage of the elevated strikeout environment at T-Mobile Park and dominate at home. However, recent track record indicates that contact-oriented hitters are the most likely players to see their offensive production translate upon acquisition by the Mariners.
Concluding Thoughts
The main question of this article was whether the park factors of T-Mobile Park put the Seattle Mariners at an advantage or a disadvantage. The truth of the matter is, that it is difficult to give a conclusive answer due to a multitude of factors. While the win-loss record does not tell the whole story, the Mariners have had a winning record at home each season since 2020 and currently have a 23-11 record at home to start the 2024 season. This would suggest that the strikeout environment at T-Mobile Park provides a net advantage to the Mariners. On the other hand, Seattle has experienced difficulty in acquiring impact offensive contributors over the past few seasons, suggesting that their home park puts the Mariners at a disadvantage as teams need to score runs at home and on the road to be successful over the course of a full season.
In my opinion, I believe that the Mariners should focus on developing pitchers who have characteristics that suggest that their arsenals will perform exceptionally well at T-Mobile Park, and it appears that the organization has emphasized this over the past couple of seasons. Therefore, I would lean in favor of suggesting that the park factors of T-Mobile Park put the Mariners at a slight advantage over their competitors. As evident by the elevated strikeout environment at T-Mobile Park, park factors can cause players to produce differently in different ballparks and can play a significant role in roster construction for major league organizations.
Photos courtesy of Icon Sportswire & WikiCommons
Adapted by Kurt Wasemiller (@kurtwasemiller on Twitter / @kurt_player02 on Instagram)