Examining Home-Field Advantage

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Examining Home-Field Advantage

• Phil Birnbaum
• www.philbirnbaum.com

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Home Field Advantage (HFA)

• In baseball, home teams generally win 54 of
  games
• Why?
• Several possible explanations

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Possible causes

• Fan enthusiasm
• Familiarity with park
• Molding team to park
• Travel
• "Home Cooking"
• Umpires
• Batting Last
• Others

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Can eliminate some

• Fan enthusiasm
• Nope. Seems to be no correlation between HFA and
  attendance
• Familiarity
• Only a little
• Travel
• Nothing significant
• Batting Last
• Not just in close games
• Pitching last also has its advantages
• See "The Diamond Appraised" and "Scorecasting"

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Recently Umpiring

• "Scorecasting," by Tobias Moskowitz and Jon
  Wertheim, released early 2011
• Claims refereeing/umpiring is the true cause of
  HFA
• Lays out some evidence for several sports

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"Scorecasting" on umpiring

• Umpires call more strikes for home team pitchers
  than for visiting team pitchers
• The higher leverage (clutchier) the situation,
  the bigger the effect
• Umpires actually favor the visiting team in
  less-important situations

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"Scorecasting" on umpiring

• Authors claim umpiring/refereeing accounts for
  almost all of HFA
• But doesn't mesh with other evidence of the
  incidence of HFA

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HFA appears in all situations

• For instance
• When one team is ahead by 4 runs early, that's
  low leverage. But HFA remains high

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Home team outscores visitors regardless
Inning Overall When one team has 4 run lead
1 18 more runs
2 10 19
3 11 10
4 8 13
5 10 9
6 8 8
7 7 8
8 6 5
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Umpires and leverage

• Mitchel Lichtman finds some effect of clutchness
  on called strike HFA, but less than
  "Scorecasting" found
• Me too

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Other estimates are lower

• John Walsh, "The Hardball Times Annual 2011"
• Home team favored by 0.8 pitches per game
• Accounts for one-third of HFA
• J-Doug, "Beyond the Box Score"
• Accounts for one-sixth of HFA
• Dan Turkenkopf, "Beyond the Box Score"
• Accounts for one-eighth of HFA

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Not just umpires?

• There might be other things going on, not just
  umpires
• How can we find out?
• Look at things that don't involve umpires

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Like what?

• Maybe fielding. Once a ball is in play,
  umpires don't control whether it's a hit or an
  out
• If defenses turn more balls into outs at home,
  would that show that HFA is more than just
  umpiring?
• No, not really. Because

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Compensating for umpire bias

• if umpires are more lenient towards home
  batters, they get more balls and fewer strikes
• More favorable counts
• Better hit balls
• Harder to field those balls
• So it could be umpiring after all!

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Compensating for umpire bias

• Similarly in other sports
• In hockey, the referee's main influence is in
  calling penalties
• Home teams outscore visiting teams even at full
  strength
• But, it could be because visiting teams have to
  play less aggressively out of fear of referee
  sensitivity
• Same for soccer, basketball, etc.

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How to tell?

• Need a measure of HFA that is not influenced much
  by umpires
• How about wild pitches and passed balls?
• Objective decision ball eludes catcher, runners
  advance

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WP/PB home field advantage

• For 2000-2009 (God Bless Retrosheet)
• Home teams
• 539 WPPB per 100,000 pitches
• Road teams
• 557 WPPB per 100,000 pitches
• 3.3 percent difference
• Statistically significant (barely)

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WP/PB home field advantage

• On 0-0 counts only
• Home 511 WPPB per 100,000 pitches
• Road 544 WPPB per 100,000 pitches
• Even larger effect

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WP/PB home field advantage

• Overall difference about 5 wins over 10 years
• Works out to .0002 wins per game
• That's 1/200 of HFA
• Runs resulting from WPPB are 1/50 of total runs
• Not perfect, but reasonable

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Basketball

• Free throw shooting percentage is not subject to
  referee bias
• HFA in foul shooting is about 0.2 percentage
  points in favor of the home team
• Difference of 120 points a year
• 0.1 points per game
• Overall HFA is 3 points per game
• Again, seems reasonable

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Speed skating

• There is a home-field advantage in speed skating!
• Of course, that can't be because of refereeing
• What could it be?

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Another theory

• For some biological reason, humans just perform
  better at home than on the road
• Testosterone levels "players may have tapped
  into a primal instinct to defend their own
  territory."
• But, whatever some intrinsic evolutionary reason
  is plausible, because
• HFA is pervasive and universal
• And none of the other hypotheses have tested out

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Competing guesses on HFA

• "Scorecasting"
• Almost 100 umpires.
• Craig Wright, "The Diamond Appraised" (1989)
• 5 crowd 5 last AB 10 familiarity 10
  shaping team to park 30 home cooking 40
  umpires.
• Me (among others)
• 10 umpires 80 intrinsic/testosterone 10
  other.

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Where to go from here?

• Need to come up with ingenious ways to decouple
  umpiring from other factors
• If you can think of any, let me know
• For now, I think there's good evidence that
  umpiring is only a small part of what's going on

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Acknowledgements

• Thanks to readers at my blog for many comments,
  suggestions, and references on this topic
• Mike Fast was especially helpful, pointing me to
  some of the studies mentioned here. Thanks, Mike.