Home-Field Advantage and Game 7

The Dodgers’ reward for having the best record in the majors this year, for recording three more wins than the Astros during the regular season, is this: they host the final game of the 2017 major-league campaign, Game 7 of the World Series, tonight.

Home-field advantage is a real phenomenon. In the game’s history, World Series Game 7 victors have been split evenly, 19-19, between home and road teams. But that’s a fairly small sample. In baseball, the home team typically wins 54% of regular-season games, and that rate holds up as a constant decade after decade, era after era.

Conventional wisdom suggests that home-field advantage is the result of multiple advantages enjoyed by the home team: the right to bat last, the ability to tailor a roster specifically to the park, a certain comfort with the surroundings, and the absence of travel-related fatigue (such as might be experienced by the visitors). All of those elements, perhaps, play a role. But the salient factor behind home-field advantage is umpire bias, particularly regarding borderline strike-ball calls. University of Chicago behavioral economist Tobias Moskowitz and Sports Illustrated writer L. Jon Wertheim documented convincing evidence in support of that observation in their book Scorecasting.

The authors used pitch-tracking data to quantify this concept.

While QuesTec, and then PITCHf/x, were created in part to better evaluate umpires and create a more uniform strike zone, and while there’s some evidence of improvement among umpires in the PITCHf/x era, the bias in favor of the home team appears to remain remarkably consistent despite year-to-year changes in strike-zone size and umpire performance.

Consider the following charts created for a post published earlier this year exploring the nature of home-field advantage. The trend lines remain more or less parallel in the years for which we have data.

What creates the bias? In the case of the home-plate umpire — just as with officials in other sports — it appears to be a desire (consciously or subconsciously) to please the crowd. Moskowitz and Wertheim demonstrate that, the more intense the environment — think Duke basketball playing at home at Cameron Indoor Arena — the more intense the bias for the home team on 50-50 calls.

So the Dodgers’ reward for the producing the regular-season’s best record is a higher probability of ending up on the favorable end of some borderline calls. Perhaps that effect will be enhanced by a raucous Dodger Stadium and its excellent sound system, which blasts sound waves from center field to the stadium’s grandstand, essentially a concrete bowl nestled within a ravine just west of downtown Los Angeles. From my experience covering games there, the stadium has excellent acoustics. It can trap and hold noise, increasing the intensity of key moments.

Jeff wrote before the series that the strike zone would likely favor the Dodgers in part because of their excellent framing tandem of Austin Barnes and Yasmani Grandal. The Astros’ less capable group is led by Brian McCann.

In preparation for this piece, I employed Baseball Savant’s detailed zones, which examine the 50-50 borderline area of the zone, to see if the Dodgers have benefited on the edge of the zone in the series’ first six games. It appears they’ve had a slight advantage as far as balls called and swings offered on borderline pitches.

Consider the following tables, with data from Games 1 through 6.

So how, if at all, should this knowledge influence managerial decision-making and player strategy in the most important of all games? We know that the road pitching staff should generally expect fewer favorable calls. So who could be more adversely affected?

As a team, the Dodgers ranked fourth in baseball in targeting those borderline zones this year (39.0% of total pitches, and 39.5% at home), while the Astros ranked 18th in pitches thrown in those borderline zones (38.4%). That’s a small percentage difference.

Of course, we’re not concerned with aggregate team totals since each manager seems to trust only a few bullpen options beyond his starting pitchers.

We know Lance McCullers and Yu Darvish are starting. We’ll see how long either lasts. Never will a leash be shorter than in a Game 7, for which almost all hands are on deck. In a series throughout which each manager has shown a willingness to bullpen, tandem, and respect the Third Time Through the Order Penalty, it stands to reason that McCullers and Darvish are unlikely to be standing on the mound for the game’s final outs.

The Dodgers should be less concerned with their nibbling pitchers at home. Dave Roberts probably has a clear plan he’d like to follow. I’d guess it’s something like this: get two quality turns through the Astros’ lineup with Darvish and then turn the ball over to Clayton Kershaw and Kenley Jansen, both of whom have excellent control (at least when not fatigued). I’d expect Barnes to be assigned catching duties, given he’s earned the lion’s share of playing time in the postseason and has been the better per-pitch framer this season (and the best in the majors per pitch).

But what about the Astros?

The following list contains the Astros’ pitchers most likely to be used tonight. They’re ranked here by their nibble factor, the percent of pitches thrown to 50-50 zones:

What we have here, essentially, is the order in which Astros’ pitchers are likely to be penalized by an away game. For instance, the Astros might want to be careful in how they employ Dallas Keuchel.

Consider, for example, Keuchel’s borderline pitch results during Game 1 at L.A:

Kuechel was able to get some calls below the zone and inside against lefties, but there wasn’t a ton of help there.

As I wrote about before the series, no pitcher throws to the borderline area of the lower zone more than Keuchel. Because of that and because of the Dodgers’ right-handed bats and their swing planes, it seemed like L.A. represented a tough matchup for the Houston lefty. That has largely proven to be true.

Keuchel should be particularly challenged on the road against the most disciplined offense in baseball. He recorded the third-lowest zone rate (37.0%) in the majors among pitchers who threw at least 100 innings this season. This is typical for Keuchel, who has lived on the edge as much as any major-league pitcher.

Keuchel has significant splits this year: a .236 wOBA at home versus a .305 mark on the road, and a 13.9-point strikeout- and walk-rate differential (K-BB%) at home versus a 12.9-point mark on the road. Keuchel is also on short rest.

In Game 1, Keuchel wasn’t able to get the inside strike against righties. Keuchel really wanted this pitch, for example:

He didn’t get it, though, and Justin Turner homered later in the at-bat.

While overthinking such decisions can cause paralysis by analysis, an umpire’s inclination to favor the home team is real and has to be considered by a manager. On this stage, the smallest of things can add up. The borderline 1-1 pitch is never more crucial. Umpire bias could play roles in shaping Game 7 and determining a 2017 World Series champion. And the Dodgers should enjoy this edge. After all, they earned it.