Baseball is a pretty idiosyncratic game. Whereas most other sports involve the fluid interaction of its participants, baseball is a turn-based contest that features a series of discrete individual match-ups between batter and pitcher. Another peculiarity of America’s past time is that every stadium’s field of play is unique. Outside of minute variations, football, basketball and hockey are all played in venues with identical dimensions. A football field is 100 yards long by 53 yards wide, a (North American) hockey rink is 200 feet long and 80 feet wide, etc.
But baseball is different. While bases are always spaced 90 feet away from each other and the pitcher’s mound is always 60 feet from home plate, the similarity of ballpark construction ends there. Some stadiums have left field fences situated 314 feet from home plate, whereas others are 347 feet. Some outfield walls are as tall as 37 feet, while others are three feet tall (sometimes in the same ballpark!).
Sometimes a visual representation best clarifies the point. The above image overlays the dimensions of Yankee Stadium onto Fenway Park. It’s almost difficult to believe that these two venues are used for the same sport! Hitting a home run to right field in Yankee Stadium is certainly easier than in Fenway, while batter’s can practically touch the left field wall in Fenway. Clearly these variations will result in a multitude of differences in how, and how many, runs are scored in each ballpark.
Beyond the obvious differences that result from wall dimensions and heights, different ballparks are also affected by the local atmosphere and weather differently. Coors Field, at an elevation of over 5,200 feet, is encased by thin air that allows the ball to travel further off the bat. Wrigley Field is routinely subject to strong tailwinds that assist in making routine fly balls into home runs, particularly in left-center field. These atmospheric conditions can have just as much, if not a greater impact, than the simple stadium dimensions.
Quantifying the effect
The end result of these park eccentricities is a palpable effect on run scoring and how those runs are scored. Yankee Stadium is actually a run-neutral environment, however it is the friendliest home run park in the league but a graveyard for doubles and triples. Fenway Park allows more runs than average, but muffles home runs and accentuates doubles.
The standard reporting to quantify these effects utilizes an index for each ballpark, with 1.00 or 100 set as average. If a park is listed with a run effect of 1.10, that means it inflates run scoring by 10%. If it has a home run effect of 94, that means it allows 6% less home runs than average.
There are a multitude of sources that evaluate park factors. ESPN’s are accessible and user-friendly, however they only show park factors on a year to year basis. FantasyPros’ figures are more robust because they take account of the last three seasons of ballpark data, which is preferred since run scoring can vary randomly in any given year. For instance, notice how in ESPN’s figures Fenway Park is the 23rd run scoring park in the MLB in 2017, but fourth in 2016 and 2015. As such, it’s always a good idea to evaluate at least three years of park factor data before jumping to conclusions.
The band boxes
As we can see, Coors Field lives up to its reputation for producing video game-like run scoring numbers. At 1.39, Coors’ run index means that 39% more runs are scored there than on neutral ground. The average MLB baseball team averages 4.7 runs scored per game. At Coors they average 6.5. Another way to appreciate this fact is to consider the Rockies’ home OPS since 2015 is by far the best in baseball at .861, but their .682 road OPS in the same span is second worst. The dimensions at Coors are actually fairly spacious and aren’t a contributing factor to its favorable run environment. In fact, the main reason that Coors is so friendly to offense is because it’s thin air allows a) baseballs to travel further off the bat and b) lower the movement on breaking pitches due to less friction in the air, allowing hitters to tee up the ball more.
Progressive Field comes in second, which is surprising because its run-altering effects are seldom discussed. Progressive’s favorable left field dimensions, which feature a short porch which extends basically all the way to center, have a likely hand in inflating home runs and doubles. Chase Field, which has the second highest ballpark elevation at 1,059 feet, and its thin desert air feature the third most run inflation. However, it probably won’t retain this status for long as the team will install a baseball humidor in 2018 that will reduce the bounce of balls off the bat, potentially reducing home runs by as much as 20%.
Fenway Park, which probably has the most unique outfield dimensions in baseball, with the shortest distance from home plate to foul pole in right field and the deepest center field area at 420 feet, comes in fourth. Interestingly, Fenway subdues home run production by 5% while inflating doubles by a massive 28%. The double inflation is largely due to the presence of the 37-foot Green Monster, which features one of the shortest left field distances to home plate and allows hitters to bang doubles off the wall with relative ease. The lower home run total results from the cavernous right field area, which hits 380-390 feet about 15 feet left of the right field foul pole.
The stingy ones
I bet most baseball fans wouldn’t have guessed that Minute Maid is baseball’s most pitcher-friendly park. It’s short left field porch is favorable to righty pull hitters, but outside of that, Minute Maid is a pitcher’s paradise with deep left-center, center and right-center dimensions. The park went through a renovation over the 2016 offseason which brought the center field fence in from an absurd 436 feet to a more manageable 409 feet, but this hasn’t had much of an effect, as Minute Maid’s 2017 run factor of 0.77 is at a three-year low.
The rest of the list is as expected. Dodgers Stadium is typically regarded as pitcher-friendly and it graded out that way since 2015, coming in second on the “stingy” list. Of particular note is the park’s suppression of triples, which occur 44% less often than in the average venue. Marlins Park’s spacious confines propel it to third on the pitcher-friendly ledger, with a 0.79 home run factor that must have hitters like Giancarlo Stanton and Christian Yelich wishing they could play for the New York Yankees (1.35 HR factor).
AT&T Park exhibits the most extreme home run to triples split in the league, with minuscule 0.64 home run factor and 1.44 triples factor. To put this one into a perspective, a 30-home run hitter in a league average park, who hits half his home runs at home, would become a 25-home run hitter just by the virtue of joining the Giants. That same hitter would hit 35 home runs in Yankee Stadium, so the swing from the best to the worst home park in baseball is an astounding 10 home runs over a full season in this hypothetical example.
Other things to consider
This primer has explored all the basics of park factors, but there are some additional things to consider when evaluating individual player statistics and performance. Firstly, the numbers presented above are a comprehensive average, taking into account what every type of hitter has done (lefties, righties, pull hitters, etc.). To focus the analysis on a specific player, one needs to consider handedness, pull/opposite field tendency and flyball/groundball inclination to develop an accurate assessment.
Consider Fenway Park. It’s dimensions are much more favorable to a right-handed pull hitter than a left-handed pull hitter due to the Green Monster’s short distance from home plate and right field’s spaciousness. Meanwhile, a primarily groundball hitter is not going accrue as many benefits from the Green Monster or bear the brunt of right field’s dimensions.
Fortunately, RotoGrinders presents park factors broken into detail for left and right-handed hitters (assuming they’re primarily pull hitters). Remember that Fenway’s overall home run factor was below average at 0.95. However, Fenway’s home run factor to left field is a robust 1.15, while to right field is a meek 0.79.
Of course, not all right-handed hitters pull the ball. Nicholas Castellanos only pulls 8.4% of his flyballs compared to 59.0% to opposite field. Unfortunately for Castellanos, Comerica Park’s large right-field results in a lot of flyball outs. He would be better served playing in a venue like Kauffman Stadium or Yankee Stadium. Meanwhile, Gary Sanchez is a flyball pull-hitter that leads the MLB in flyball pull percentage, meaning that he is probably happy to hit at Yankee Stadium. However, if Sanchez played in Fenway he would put up even gaudier statistics.