Why home field advantage does matter in this year's playoffs

At this point, it looks like the Royals won't have home field advantage. Some people think that's not a huge deal, even a co-writer on this site agrees. We all like each other as people, but don't have to agree with one another. I don't think it's a huge deal, but it is very advantageous to have home field advantage, and for several reasons.

First we know home field advantage exists and for different reasons:

It appears that home teams do pretty much everything better than road teams. They hit the ball more, they hit the ball harder, they throw more strikeouts, and they surrender fewer walks. Home teams prevent triples more frequently, and record double plays more frequently. They record more outs on balls in play, and they make fewer errors.

The extra home-field advantage in the first three innings strongly suggests comfort and familiarity are significant factors in home-field advantage. The large effects within the strike zone indicate that the mound and the batter's eye are things that pitchers and hitters are more comfortable with at home. The extra triples surrendered on the road strongly suggest an impact of stadium familiarity in home-field advantage. The extra stolen bases indicate reaction time may also be playing a role. All of these numbers together indicate a large significance of mental aspects that are not quite emotional, but affect things like eyesight, reaction time, and learning about the home turf. That pretty much answers the question of what home teams are doing better.

Home teams see about a 4-5% boost in their win expectancy to start the game (before taking lineups into account). That's roughly the equivalent of starting the game off with a runner on base. That's might not ever amount to a run, but that's not nothing.

In the Royals Review unpublished vault, I began writing an article where I used SaberSim (an excellent website) to simulate the outcome of the Royals series against possible playoff opponents. It started out a novel idea I thought. Simulate each game of a series 1,000 times with the most used lineup and plugging in pitcher vs. pitcher match ups. For what I could find, SaberSim simulates games using a multitude of factors:

SaberSim provides daily, matchup-specific projections by simulating (thousands of times) each game scheduled for a particular day. The Sim matches up the specific lineup of each team against the specific starting pitcher (and bullpen) of each opposing team. The simulated games then operate as actual baseball games operate, and each individual plate appearance is simulated until each game is complete, at which point the process is repeated. After the matchups have been simulated thousands of times, the results are presented in the form of graphs and tables that display a detailed breakdown of the performance of each player and team involved.

Specific Context includes:

Projections, Last Season Stats, Current Stats, Etc.
Exact Starting Lineups, Starting Pitchers, and Closers
Matchups Updated as Daily Lineups are Released
Precise Batting Orders
Quantifies Each Hitter's Effect on the Hitters Around Him
Detailed Ballpark Factors, Specific to:
Batter Handedness
Hit Type (1B, 2B, 3B, HR)
Strikeouts, Walks, and more
Batter-Pitcher Platoon Splits
Handedness Matchups
Home/Away
Pitching Changes based on Running Pitch Counts
Removes Guesswork re: Projected Innings Pitched
And Much More

So I started plugging in lineups, matching pitchers, simulating the games, and building incredibly simplistic and caveman-esque excel graphs of the outcomes (I simulated each game 5,000 times in 1,000 game buckets). As I started my way down the list I eventually found a fly in the ointment: the home team won every time. I mean every time.

I figured...okay, this might not be right. What am I doing wrong? I then reached out to Matt Hunter (who's a great Twitter follow and owner of SaberSim) to see if I'm being my normal dumb self.

@Shauncore There is a home/away adjustment, so even if the exact same teams are matched up against each other, the home team will win ~55%

— Matt Hunter (@MattR_Hunter) August 12, 2015

Now I know this is just a repetition of what I said above, but the home team has a legitimate advantage just by showing up at the their ballpark. We know this both historically and through the simulation adjustment as described by Matt Hunter.

One thing I want to look at is the Royals platoon splits by batted ball location, or how the different handedness hits to each location. The effort is to look if the Royals handedness would help or hurt them in different parks. For instance if the Royals' right-handed batters hit the ball well to left field, you'd want them in a park that is neutral or even better helps right-handed batters to left.

Here's how the Royals hit overall (not park specific) to each part of the outfield.

The Royals left handed power is above average across the board there, but they are also below average in right handed power (by batted ball location factors at least). It's almost at a 100 basis point difference on all three locations.

Now by the two possible parks they could play the ALCS at (assuming the Jays/Royals make it that far)

Kauffman Stadium

For right handed batters they hit near their normal rates at home as equal on the road except for center. However their left handed power is suppressed at home. Home runs are heavily suppressed to begin with at Kauffman (ISO is more than just home runs of course) but it seems counter intuitive to the park factors for Kauffman (normally is a bit worse for lefties) the Royals lefties have hit worse.

Rogers Centre

Legend:

Neutral ISO - The Royals ISO both home and away

(Kauffman ISO) - The Royals ISO at Kauffman

*Lg Avg at park - the league average at the park

^ Team ISO - How the opposing team does at their own park

The Blue Jays right handed batters hit worse than league does at their park, but the Royals neutral right handed power is still far behind both here.

The Blue Jays were once very righty heavy, but they've added some left handed/switch hitting bats to even things out. Those left handed bats have hit very well to center and pull power and close to even to the league average at home.

When you compare the different splits to league average with each point +/- 100 being 1% better/worse than average:

ISO+	RF Neutral	RF Kauffman	RF Rogers
TOR LHB	86	X	98
KC LHB	108	103	X
TOR RHB	145	X	72
KC RHB	64	104	X

ISO+	CF Neutral	CF Kauffman	CF Rogers
TOR LHB	34	X	54
KC LHB	111	116	X
TOR RHB	140	X	121
KC RHB	66	103	X

ISO+	LF Neutral	LF Kauffman	LF Rogers
TOR LHB	116	X	105
KC LHB	126	100	X
TOR RHB	128	X	111
KC RHB	82	94	X

The Blue Jays have a ton of right handed power, and it plays well at their park in all directions for them. If they get home field advantage, which is looking more inevitable by the game, then they'll get an additional two (possible) games to use that power. The Jays will start with an extra 4-5% advantage and the first two games will be at a park where they are ~20% better (125 wRC+ at home, 106 wRC+ away).

Again...home field advantage isn't the deciding factor, and the Royals made it to the World Series last year beating two teams on their own turf, but it's something.