Park factors: They're often cited, sometimes exaggerated, occasionally misunderstood.
A player's home environment can have a noticeable impact upon his statistics, whether it's the ballparks' differences in terms of outfield-fence measurements, fence heights, foul territory, playing surface, altitude, climate or impact of the structure itself upon said climate. Even the slightest difference can have a tangible effect.
That said, the danger in overstating park factors' impact is treating them like the driving force behind a player's performance rather than a contributing trait. Consider that, in the past five seasons combined, New York's Yankee Stadium was 63 percent more favorable for home runs than was Miami's Marlins Park, which means that for a 40-homer hitter, it meant a benefit of between 12-13 home runs (40 divided by two for the home games times 0.63). While that might seem like a lot, remember that's cherry-picking two ballparks that reside at the extremes in that singular category, and that home runs tends to have one of the wider ranges of any statistical category.
By the way, Giancarlo Stanton made the move before last season from one of those parks to another, traded by the Miami Marlins to the New York Yankees, and actually hit fewer home runs at Yankee Stadium (20) than he had at Marlins Park the year before (31). That demonstrates that it's not a hard and fast rule.
Still, it's important to know the benefits (and drawbacks) that a player's home ballpark provides him, in order to gain any edge possible.
We provide these annually on ESPN.com on our Park Factors page, but that doesn't tell the entire story. Certain ballparks are more susceptible to year-over-year variance than others -- Chicago's Wrigley Field, due to the randomness of wind velocity and direction on a game-by-game basis, is an obvious example -- so it's wiser to calculate these numbers over a lengthier period of time. Five years seems much more appropriate.
First, two ballparks underwent significant, fantasy-relevant changes last season, and another opened its doors for the first time in 2017. Reviewing special circumstances such as these is an important annual exercise.
Revisiting Chase Field's humidor, introduced in 2018
As mentioned in this space last season, the Arizona Diamondbacks installed a humidor following the 2017 season, in order to store baseballs at a constant humidity level in order to battle the effects of high altitude and temperatures on the games played in Phoenix. While a single year of park factors under new playing conditions isn't enough to pass sweeping judgment, one thing was clear: The humidor had a significant impact upon how Chase Field played in 2018.
What was once an extreme hitters' park morphed into a much closer to neutral environment, with some of the venue's park factors suggesting it had actually become pitcher-friendly -- something some analysts predicted in advance of 2018 (you can read up on a few of them in the link in the previous paragraph). It was a much more middling park for power, with a 0.935 home runs park factor that was almost evenly balanced between left- and right-handed hitters. Here's a comparison of Chase Field's park factors in 2018 versus the five years that preceded it.
A caveat: again mentioned in this space last season was Chase Field's year-over-year inconsistency in terms of park factors, grading one of the 10 most variable by season in terms of runs scored. There's a good chance the final ruling on the humidor's impact upon Chase's offense might not be fully known for a half-decade, though it's clear that some degree of adjustment needs be made for Diamondbacks players. This is the primary reason that Paul Goldschmidt's trade to the St. Louis Cardinals wasn't a catastrophic one from a park-factors perspective, because Busch Stadium was actually not much less homer-friendly in 2018 (0.870, 24th) than Chase Field (0.935, 20th) was.
Revisiting Angel Stadium's shorter outfield fences, adjusted in 2018
The arrival of Shohei Ohtani in Southern California conveniently coincided with the Los Angeles Angels' decision to lower the home-run line on the outfield fences in right and right-center fields, dropping from 18 to 8 feet. While Ohtani enjoyed an outstanding U.S. debut season in his own right, the adjustment made by the team had a profound impact on the overall power numbers at the ballpark. Again using the 2013-17/2018 comparison:
Angel Stadium actually ranked the game's No. 6 ballpark in terms of home runs last season, and it was the No. 1 venue in the game for home runs by left-handed hitters. Ohtani, who hit 15 homers there compared to seven on the road in 2018, had a significant say in that, though, and it remains to be seen whether the ballpark will play at quite an extreme level in Year No. 2.
Still, it's great news not only for him but also left-handed free-agent signee Justin Bour, who has the power-oriented game to capitalize if the ballpark plays similarly. Kole Calhoun, who hit 16 of his 19 home runs from July 1 forward, could also benefit as he continues to shift his game to being more fly ball-oriented.
SunTrust Park completes Year No. 2 of existence
The Atlanta Braves' now-two-year-old SunTrust Park was analyzed in this space last season, covering its first year of existence, with much of the same caution offered with the previous two ballparks regarding investing too heavily upon one year's worth of data. With two years now in the books, our takeaways are at least slightly stronger.
SunTrust Park seems to be playing as a neutral environment, with an ever-so-slightly-better leaning than its predecessor, Turner Field. Last season, it experienced a greater runs scored factor -- 1.120 to 0.976 -- but a lesser home runs factor -- 0.794, down from 0.953 -- than it did in 2017. Combining the two seasons and comparing it to Turner Field's rates in its final five seasons (2012-16) gives us this:
Not a whole lot seems different in Atlanta other than SunTrust is a slightly more favorable run-scoring environment, but with it lacking the puzzling boost in terms of pitcher strikeouts that Turner used to enjoy, with things like foul territory, the batter's eye and climate being as good guesses at the reason as anything. If there's any takeaway here, it's that SunTrust does represent a downgrade in terms of home run factors for free-agent signee Josh Donaldson, who trades Toronto's Rogers Centre (1.067 home run factor from 2014 through 2018, 10th) for SunTrust.
All 30 ballparks' park factors as well as players of note
If you're curious about the park factors for specific ballparks from the past five seasons, the full charts are available at column's end, covering runs scored, home runs (including left- and right-handed splits), BABIP (batting average on balls in play), doubles and triples (impact on extra-base hits), walks and strikeouts.
Here are some key findings within these park factors, focusing primarily on players who changed teams during the offseason:
Manny Machado's late decision to sign with the San Diego Padres dropped him into a scenario where fantasy managers might misinterpret the impact of park factors upon his statistics, as I wrote here. After all, many of us might still believe that Petco Park, the Padres' home, remains one of the game's most pitching-friendly environments. It's still a pitching-friendly ballpark, but not nearly as much as it was before the team brought in the outfield fences (mostly in right and right-center fields), and in 2018 Petco was actually the 14th-most-favorable park for home runs (1.020 factor). Was last season the new norm for the venue, or might it regress to its 0.929 number from the past five years (2014-18) combined? The answer to that question will have a bearing on Machado's fantasy potential, though I don't think it was a bad landing spot.
Perhaps no player enjoyed a more under-the-radar change regarding his park factors than J.T. Realmuto, who traded Marlins Park's worst-in-the-majors right-handed home run factor (0.715 from 2014 through 2018) for Citizens Bank Park's best-in-the-majors 1.294 home run factor for righties. The Philadelphia Phillies might've landed themselves a gem with the trade, and at the very least, Realmuto should benefit greatly simply by escaping Marlins Park, where he was a .245/.294/.384 career hitter with a 2.2 percent home run rate, compared to .309/.356/.492, 3.2 percent, on the road.
Bryce Harper also benefitted from the move from Washington to Philadelphia, even if the contrast between those cities' ballparks wasn't as stark as between Miami and Philadelphia. From 2014 through 2018, Citizens Bank Park was the eighth-friendliest venue for home runs from left-handed hitters, with a park factor of 1.142, while Washington's Nationals Park was 22nd-best for lefties, with a park factor of 0.915 (and it was 18th in terms of home runs by all hitters with 0.991). Harper's decision to sign with the Phillies seemed tied to preferring the ballpark, and there's an excellent chance he'll be able to once again reach the 40-homer plateau at some point in the next couple of seasons there -- he might in fact log several of them.
Andrew McCutchen should similarly benefit by signing with the Phillies, considering that he played the bulk of his big league career to date at Pittsburgh's PNC Park, which ranked 28th with a 0.756 right-handed home run factor from 2014 through 2018, and San Francisco's Oracle Park, which ranked 29th with a 0.734 righty homer factor.
Coors Field is renowned for being an extreme hitters' park, with everyone well aware of what its mile-high altitude does to a batted ball as well as to the break on a pitcher's offerings. What tends to be overlooked: Coors is by far the best venue in the game for BABIP (batting average on balls in play), inflating it by a good 15 percent, mainly because of its spacious, largest-in-the-majors outfield territory. It's not the power hitters who benefit most there, but rather the gap-hitting, line-drive-and-fly-ball-oriented bats who do, which is why Daniel Murphy's decision to sign with the Colorado Rockies made for a dream fit.
Yasiel Puig has been a popular breakthrough candidate in the fantasy industry in early-winter drafts, with much of the reason being his move from Los Angeles' Dodger Stadium to Cincinnati's Great American Ball Park (the remainder his strong finish to the 2018 regular season and postseason). There could be something there, considering Dodger Stadium ranked 18th with a 0.977 home run factor for right-handed hitters the past five seasons combined, while Great American Ball Park ranked fourth with a 1.149 factor from that side of the plate.
Yasmani Grandal enjoyed one of the more under-the-radar park factor benefits among free agents who changed teams this winter. Yes, Dodger Stadium was the sixth-best home run park for left-handed hitters from 2014 to 2018 (1.181 factor), but it was only 11th overall in the category (1.061) and he's a switch-hitter. Milwaukee's Miller Park was the fifth-best venue for home runs by all hitters from 2014 to 2018 combined (1.163), and it had a park factor at least 11 percent greater from either side of the plate than Dodger Stadium.
Announced ballpark changes for 2019
Here is an overview of all reported ballpark changes since the end of last season, all of which seem more cosmetic in nature:
Chase Field, home of the Arizona Diamondbacks: The team installed synthetic grass during the offseason, replacing the former natural-grass surface.
Marlins Park, home of the Miami Marlins: The team removed its infamous "home run sculpture," naturally inspiring hitters to hit a whole lot more home runs since they no longer will have to watch the sculpture in action (kidding, kidding!), replacing it with a more fan-friendly viewing area in center field. No adjustments to either the outfield fence heights or distances were reported along with the decision.
Oracle Park, home of the San Francisco Giants: The team replaced its scoreboard in center field with a new one more than three times the size of the original.