Home Field Advantage & The Five-Run Rule

Home teams are doing famously well this year. I can't pinpoint a cause like some intrepid accusers, but I can give the numbers:

Home teams: 672-511 (.568)
Away teams: 511-672 (.432)
Home team runs on average: 4.68
Away team runs on average: 4.37

The home team therefore has a 13.6% better chance at winning the ballgame, using 0.31 more runs on average to do so. We've already cited Cy Morong's Historical Trends in Home Field Advantage as a good source of HFA history, and it bears noticing that the average home field advantage is around 10%. Given baseball's long seasons, adding 3.6% more to HFA is equivalent to almost 6 more wins. That's the difference between playing in October and going home.

In other news, teams who have scored 5 runs or more in a ballgame this season have gone 465-90 (.838). If you play in one of the 47% of games in which one team scores at least 5 runs, it better be you. If it's not, you have less than a 20% chance of winning the game.