How Important Is Home Field Advantage?

Originally published at DFSEdge.

I’ve touched on the existence and importance of Home Field Advantage briefly in the past, and I make frequent mention of it in my Strong Play articles, but we’ve yet to really dig in to see exactly how relevant of a factor it is.  A recent tweet from reader Greg Richards (@GRich25) has bumped home field advantage up on my to-do list, so today we’re going to check it out.

In mentioning why I wasn’t too crazy about Mike Minor against the Nationals a couple days ago, I brought up how Minor would be on the road.  Greg replied with, “Is there data somewhere to support that? Intuitively that seems of less importance to me in baseball.”  I noted that, while the crowd or extreme weather may play a more important role in, say, football, that one could hypothesize that home field advantage is “more important in MLB since NFL/NBA/NFL fields are all pretty uniform.”  The three point line is always the same distance from the hoop.  The red zone is always 20 yards long.  Something about hockey.

In baseball, though, no two parks are the same.  The infield diamond is uniform and the foul lines are straight, and that’s about it.  Outfields, fences, foul ground, everything else is different. I’d actually wager that the more unique a park is, the more advantage the home field gains.  It’s a lot easier for Brandon Barnes to navigate that hill in center field than it is for Leonys Martin when he visits Minute Maid.  I may try to look at this in the future, in addition to a few other HFA iterations that I have suspicions about, but for today we’ll stick with the basics.  Does home field advantage exist, and if it does, to what extent?

Home Field Advantage for Hitters

You can get a rough estimate for home field advantage just by comparing league-wide home and road numbers, but when there’s a better method that’s going to give us more accurate results, I like to use it.

Warning: Boring Methodology Ahead. Skip Ahead If You Just Want the Results.

To determine home field advantage, I focused on a recent three-year stretch of data and compared each individual hitter’s line in his home park with every individual road park he played in that year.  I then take a weighted average (using the harmonic mean of a player’s plate appearances in his home and road park pair as the weight to combat sample size issues) of all of these data points to find how much differently hitters perform between their home and a random road park.  While it doesn’t make much of a difference, I’ve also park-adjusted all the relevant stats using my own platoon park factors.

It’s Safe to Come Out Now.  Boring Methodology Section Over.

Now onto the fun part: the results.  Below is a table with seven stats and the differences between them when a hitter is at home versus on the road.

Home Field Advantage for Hitters
0.008 0.012 0.017 0.029 0.2% -1.0% 0.4%

As you can see, home field advantage absolutely exists, but the results are relatively modest.  A player will hit eight points better at home than he will on the road and OPS nearly 30 points better.

Home Field Advantage for Pitchers

Because of some data issues, the pitcher numbers weren’t park adjusted.  For hitters, the park adjustment reduced the effects by 10% on average, so keep in mind that these effects may be slightly overstated.

Home Field Advantage for Pitchers
-0.013 -0.016 -0.026 -0.042 -0.3% +1.0% -0.6%

The results for pitchers are larger than they are for hitters but still relatively modest.  Pitchers cut 13 points off their batting averages and, perhaps most notably, add a point to their strikeout percentage.

Closing Thoughts

When accounting for home field advantage, don’t make the mistake of taking the full figures in the tables above off of a player’s full-season line.  A player who is hitting .308 overall this year will not hit .300 on the road.  You have to cut that .008 figure in half since his seasonal line is composed of both home a road games.  So a .308 hitter overall would hit .304 on the road and .312 at home.  That limits the usefulness of including home field advantage to decide which hitters to draft, but the effects are there and are worthwhile to include in a comprehensive evaluation of the contextual factors facing a player on any given day.