The 2019 season will be remembered for its dramatic rise in home runs, perhaps the product of the composition of the baseball itself, but it also had an unusual effect: Park factors for the 30 teams' home venues had perhaps the flukiest single-year results in the game's history. Yankee Stadium played as a pitchers' park? It sure did.
Perhaps that'll also cement an important lesson cited annually in this space: One-year park factors are notoriously unreliable, based off altogether-too-small sample sizes, and a five-year outlook is a much better gauge of their impact.
As is, park factors as a whole are often exaggerated, if not widely misinterpreted, among fantasy baseball managers. Even a five-year outlook has its pitfalls.
For those new to the topic, "park factors" are statistical gauges of a ballpark's influences on various baseball outcomes, like runs scored, home runs, hits and, yes, even strikeouts. Since all 30 teams' home ballparks have varying dimensions -- the distance to the outfield walls in all directions as well as the outfield fence heights and the amount of foul territory -- as well as playing surfaces, altitudes and climates, there can be a statistically advantageous trait in most every ballpark in which baseball is played.
In order to calculate these park factors, we take the per-game rate of each statistic by both the home and road teams at a certain ballpark, then compare it to the per-game rate of the same statistic by both of those teams in all their games played in every other ballpark around the majors. A park factor of exactly one (displayed as 1.000 in the chart at column's end) means that the ballpark had a neutral effect on that statistic. Anything greater than one means the ballpark improved that statistic and anything less than one means it suppressed it, and the difference compared to one is the percentage by which that ballpark improved or suppressed that statistic.
For example, if the Arizona Diamondbacks and Atlanta Braves play three games at Arizona's Chase Field, scoring a combined 16 runs, and three at Atlanta's SunTrust Park, scoring a combined 11 runs, and that represented the entirety of their seasons, then Chase Field's park factor for runs scored for that season would be 1.455 and SunTrust's would be 0.688, meaning that Chase Field inflated home run production by 45.5% (1.455 minus 1 times 100) and SunTrust deflated it by 31.3%.
With that in mind, here's why last season was such an unusual one:
New York's Yankee Stadium, the majors' most homer-friendly venue in the five seasons that preceded it (1.298 home run factor from 2014 to '18), was the 13th-least homer-friendly ballpark in baseball in 2019. It was also the second-worst environment for runs scored (0.816), after having been above-average from 2014 to '18 (1.030).
Miami's Marlins Park, baseball's worst run-scoring environment from 2014 to '18 (0.808 runs scored factor), was the game's sixth-best venue for runs scored (1.087).
Boston's Fenway Park went from being one of the best ballparks in baseball for hits (1.084 factor from 2014 to '18, second-highest) to merely a league-average one (0.992).
Granted, every season in baseball's history exhibits unusual year-over-year ballpark trends, but these three in particular stood out for how entirely out of character they were for the three venues in question: Yankee Stadium, since its opening in 2009, has been a homer heaven for hitters, especially those who bat left-handed. Marlins Park has been a cavernous, pitching heaven since its opening in 2012, even after the team shrunk its outfield dimensions following the 2015 season. Fenway Park, with its "Green Monster" that measures the closest to home plate of any left- and left center-field fence in baseball, has a reputation for inflating hit totals, especially from right-handed hitters.
This is one area where the discussion centering on the composition of the baseball itself entering 2020 -- one where we won't have any concrete data from which to judge in time for our drafts -- is such an important one. If the baseball used in 2018 returns, might these venues' park factors settle closer to their 2014-18 five-year norms? Or are park factors now subject to wild, annual fluctuations and less valuable from a player-scouting perspective? Only time will tell.
If you'd like to judge for yourself the relevance of 2019, single-year park factors, my full calculations can be found at column's end, beneath the five-year park factors chart -- that being the one to trust most.
Speaking of Marlins Park, it's one of three ballparks that have endured noticeable changes for 2020, either a change to its outfield dimensions and/or fence height -- San Francisco's Oracle Park joining Marlins Park in that category -- or the venue being replaced altogether -- Texas' Globe Life Field encompassing that category, as it replaced the previous Globe Life Park during the offseason. Here's a quick look at the changes as well as what to expect from each:
Miami's Marlins Park changes
Marlins Park endured a change in outfield dimensions during the offseason, in an attempt to boost its run-scoring environment. The outfield fence distances were shortened by 7 feet to straightaway center field, reduced from 407 to 400 feet; and 5 feet in right-center field, reduced from 392 to 387 feet.
It's a small change, similar to the one the team employed in 2016, when it shrunk the center-field measurement from 418 to 407 feet while lowering the fences by roughly 3 feet all around the ballpark. That one had only a slight impact on game play: it boosted the venue's home run park factor from 0.698 during its first four seasons of existence (2012-15) to 0.768 during its next four (2016-19), but actually decreased its run-scoring factor from 0.998 to 0.839 comparing those same four-year time spans.
As this year's changes alter more of the measurements to the right of dead-center field than to the left of it, left-handed hitters might see a greater overall boost. New acquisitions Corey Dickerson and Matt Joyce, both of whom bat left-handed, should benefit more than fellow new Marlin Jesus Aguilar, who is right-handed.
That said, expect Marlins Park to remain an extreme pitchers' venue, considering its measurements remain among the deeper in baseball -- center field being moved to roughly a league-average distance is the only one that is not. Players like Aguilar and Jonathan Villar, who have spent the majority of their recent careers calling significantly more hitting-friendly ballparks their homes, probably won't benefit as much as it seems, and certainly not just from hearing, "Oh, the Marlins moved the fences in."
San Francisco's Oracle Park
Oracle Park -- formerly named Pacific Bell Park (2000-03), SBC Park (2004-05) and AT&T Park (2006-19) -- made significant changes during the offseason to improve its run-scoring environment as well as the fan experience, relocating the bullpens from foul ground along the outfield lines to center field and outside the field of play as well as bringing in and lowering the fences.
The outfield fence distances were shortened by 5 feet at the deepest point in left-center field, reduced from 404 to 399 feet; 8 feet to straightaway center field, reduced from 399 to 391 feet; and 6 feet in "Triples Alley," the deepest point in right-center field, reduced from 421 to 415 feet. In addition, the fences in left and center fields were reduced from 8 to 7 feet in height.
While that's only a minor, potentially cosmetic change, just as those done to Marlins Park, these are still the more significant adjustments of the two venues if only because of the impact upon what was by far baseball's most pitching-friendly environment in recent seasons. Taking a five-year look at Oracle Park, it was baseball's worst venue for home runs from 2015 to '19 (0.671, which was nearly 11% tougher on the category than any other ballpark) and fourth-worst for runs scored (0.897). Last season alone, Oracle ranked dead last in both categories (0.690 home runs factor, nearly 5% tougher than any other ballpark, and 0.798 runs scored factor).
With these changes, it's possible that Oracle Park might now merely challenge for the honor of "toughest home run ballpark in baseball," rather than run away with that crown, as it has for several years now. But the Giants have another problem similar to that of the Marlins: Not many of their players are especially fantasy-relevant in ESPN standard mixed leagues, and the potential boost to players like Brandon Belt, Evan Longoria and Mike Yastrzemski probably won't be enough to register in terms of draft-day fantasy stock.
Tuck away these two ballparks' changes as more relevant to your daily-fantasy or streaming starter strategizing, where opposing pitchers (and, to a lesser extent, hitters) might see more of an impact upon their performances.
Texas' brand-new Globe Life Field
How confusing might this be? The Texas Rangers, who opened Globe Life Park (then The Ballpark in Arlington) in 1994, just replaced it with the new Globe Life Field, which sits directly across the street from the old venue. That's right, this team picked up and moved roughly 750 feet, trading the "Park" for "Field" in its new stadium's name.
That's not to say that, inside the stadium, things will play precisely the same. The Rangers altered the outfield fence measurements in their new home in tribute to some of the franchise's most influential individuals. Globe Life Field will measure 329 feet to left field, in tribute to Adrian Beltre; 372 feet to left-center field, to honor the franchise's first season in Arlington in 1972; 407 feet to straightaway center field, in tribute to Ivan Rodriguez; 374 feet to right-center field, to honor the 1974 "Turnaround Gang," and 326 feet to right field, in tribute to manager Johnny Oates. It will also have a 410-foot measurement to the home and visitors bullpens to the left and right of straightaway center, in tribute to Michael Young.
These measurements make the new venue noticeably smaller to left- and left center-field than the previous one, as well as closer to home plate than the league's average everywhere except the center- field expanse. Even there, it only narrowly qualifies as one of the 10 deepest ballparks in the game, so it's not like there's significant threat of the new ballpark leaning pitching-friendly.
One aspect we can't gauge regarding the new park, and one that was a huge influence at the Rangers' previous home, is the impact of wind currents within the stadium. That was considered one of the factors in making Globe Life Park one of the most favorable hitters' environments in the game. But with no promise of those remaining in the new Globe Life Field, it's foolish to regard the new venue as a lock to be as hitting-friendly as its predecessor.
The smart move is to regard Globe Life Field a top-10, rather than top-three, hitters' venue, though the odds are great it's going to lean toward the hitting side. Still, any shift closer to center is a positive for a pitching staff that got solid seasons out of Lance Lynn and Mike Minor and added Corey Kluber, Kyle Gibson and Jordan Lyles during the offseason. Don't be so fearful of Rangers pitchers entering 2020 as you might have in the two-plus decades that came before it.
All 30 ballparks' park factors
If you're curious about the park factors for specific ballparks from the past five seasons or for 2019 alone, here are the full charts, covering runs scored, home runs (including left- and right-handed splits), hits, extra-base hits and strikeouts. The first chart, which is the handier resource, covers the 2015-19 seasons combined, while the second chart covers only the 2019 campaign.