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If you have ever selected a streamable pitcher based on home park or benched an otherwise must-start arm at Coors Field, you already know how much a stadium can impact a player's bottom line.
Ballpark Factors quantify the influence each stadium has, allowing you to make the most of your fantasy team's real life schedule.
Today, we continue our journey through baseball sabermetrics with a look at how each team's home stadium can play a factor in the fantasy baseball world.
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How to Interpret Ballpark Factors
Ballpark factors are set to a base of 100, meaning that a park factor of 100 plays perfectly neutral. Factors greater than 100 signify that a given park allows more of that outcome, while numbers below 100 represent less of those outcomes.
There are multiple sources of ballpark factors, including FanGraphs, Baseball Prospectus, ESPN, and Statcorner. Each calculates their numbers a little bit differently, but they all use the base-100 scale listed above. There is no "correct" factor to use, as each system has its own merits. Just make sure you stick to a single source for any analysis to control for the variance.
The source you choose also dictates how much each point above or below 100 is "worth." A player only plays 50% of his games at home, with the rest of his schedule comprised of road games. Fangraphs halves all of their factors to accommodate this, making each point above or below 100 represent a one percent increase or decrease over a full season of stats. Other sources leave that job to you, making every point worth two percentage points in a player's final line.
If that's too confusing, it's fine to forget it. The only thing you need to know is that a park factor of 110 is considerably higher than a 105 mark.
When most fantasy owners think of ballpark factors, they think of homers. A park allowing plenty of bombs is viewed as a hitter's park, while parks allowing fewer dingers are more pitcher-friendly. Let's consider Yankee Stadium as an example.
Yankee Stadium is known as a home run haven for good reason. In 2017, the stadium had a Fangraphs HR factor of 112. However, this does not mean that the stadium played exactly the same for all hitters. The short porch in right field helps left-handed hitters (124 per Baseball Prospectus) more than right-handed hitters (111), creating a meaningful platoon split in how the park plays. Of course, a right-handed hitter with an opposite field power stroke could benefit like a lefty. The point is that all ballpark factors should be considered with nuance.
While most fantasy owners are familiar with certain ballparks allowing more or less homers than others, BABIP is an under-appreciated component of ballpark factors. Altitude, infield conditions, foul territory, batter's eye, and the size of the stadium can all influence how a ballpark plays beyond just home runs.
For example, the Colorado Rockies managed a .351 BABIP at home last season against a road BABIP of .311. Likewise, they posted a .348 mark at home vs. .302 on the road in 2016, .346 against .276 in 2015, and similar differences in every other season at Coors Field. Players tend to perform a little better at home, but Colorado's splits seem indicative of more than that.
Indeed, Coors Field promoted more singles (109 per FanGraphs), doubles (also 109), triples (132), homers (110), and line drives (107) than the average park in 2017. The sample size of triples is usually too small to mean anything, but Coors Field has many quirks to help explain its extreme offensive environment.
It's a gigantic ballpark, offering plenty of real estate for balls to find grass. Pitchers claim that breaking balls behave differently due to the elevation of the Mile High City, removing some of their weapons. Fatigue may set in faster for the same reason. The introduction of the humidor has decreased the ballpark's HR rates compared to the complete bandbox it was at the height of the Steroid Era, but it still consistently posts the highest BABIPs in baseball. For this reason, fantasy owners should be skeptical of Colorado hurlers.
Colorado is the most extreme example, but every stadium has some quirk that makes it unique. Fenway's Green Monster, the Trop's artificial surface, and the miles of foul territory in Oakland all affect a player's fantasy stats.
That said, sometimes ballpark factors can lie. Eighty-one games is a relatively small sample size, so a park could play dramatically differently in a given season than it has in the past or should be expected to moving forward. FanGraphs offers a five-year average park factor for overall scoring environment that eliminates much of this noise.
If you're curious, Coors Field is well above other offensive parks with a five-year average factor of 116. Second place Arizona and Texas are tied with 105. Petco Park and Citi Field (95) are tied for most pitcher-friendly stadium. Obviously, you should pay more attention to the current year's data if there is a reason to believe the park changed. For instance, the installation of a humidor at Chase Field likely renders Arizona's previous ballpark factors moot.
Finally, it's worth noting that any ballpark factor worth looking at has a procedure in place to avoid being influenced by the home team's standout performers. For example, we have previously seen that Byron Buxton of the Minnesota Twins is an outstanding defensive outfielder. This fact does not slant Minnesota's ballpark toward pitchers because the performance of visiting teams in Minnesota is compared to their performance against Minnesota, not the league at large. Thus, a player like Buxton is not a variable.
Conclusion
Ballpark factors quantify how much influence a player's environment has on his final totals. A 100 factor is league average, with numbers above or below that indicative of more or less of whatever it is a factor for. Most fantasy owners think of homers when considering park factors, but singles, line drives, and even strikeouts have park factors as well. Platoon splits can also dictate where a given player is most likely to succeed.
