Home Field Advantage, Measured

Home teams win more often than road teams in every major sport. The size of the edge differs substantially: it is largest in sports with heavy travel and loud, close crowds, and smallest in sports where the playing surface is standardised and the officiating is tightly controlled.

The important framing is that home advantage shifts a probability by a modest amount. It is a thumb on the scale, not a different scale.

What people call home field advantage is a bundle:

• Travel and rest — the road team may have crossed time zones or played the night before.
• Familiarity — the surface, the sightlines, the altitude, the routines.
• Crowd effects on officiating — the best-documented single component in several sports.
• Rule-based advantages — batting last, last change, the ability to match personnel.

These are separable, and knowing which one is doing the work tells you when the advantage should be larger or smaller than usual.

Because it is a bundle, home advantage is not constant. It shrinks in neutral-site games, in empty or half-empty stadiums, and in matchups where the road team has had extra rest. It grows with altitude, with unusual surfaces, and with long road trips.

The lesson generalises: whenever a factor is really several factors, ask which ones apply tonight rather than applying the league-wide average to every game.