Tennis Desk Research · Marin & San Francisco USTA NorCal · Adult league

The home team wins 55.8%, and a fifth of that is the visitors not turning up

Yes, and by more than most people guess: the home team won 55.8% of 15,445 decided team matches in Marin-area and San Francisco USTA NorCal adult league, every season from 2022 to 2026.

Then I asked what else could produce it, and the answer is more interesting than the number.

Before the chart, the catch

A team match is several lines played at once, and a line where a side names no players is awarded rather than played. Those lines count in the result exactly like played ones, and the side that arrives short is usually the one that had to drive. Part of what follows is that, rather than tennis.

The same question, cut four ways

every match
55.8 · n=15,445
All decided team matches. Ties are left out: they have no winner.
both sides full
54.6 · n=13,533
Neither team left a line unfielded — the closest thing here to tennis played on the merits.
someone short
63.7 · n=1,912
At least one line where a side named no players at all.
split home-and-home
58.6 · n=893
The same two teams, once at each venue, both fully fielded, and they split. Team strength cancels exactly.
Share of decided team matches won by the side listed at home, per hundred. The axis starts at 50, because 50 is what no home advantage looks like. Seasons 2022–2026.

A fifth of the margin is not tennis

1,912 of the 15,445 matches contain at least one line where a side named no players, and on those 2,325 lines the home side won 65.4%. The team that arrives short is usually the one that had to drive.

Take those matches out and the home rate falls from 55.8% to 54.6%, a fall of 1.12 points — 19% of the whole margin over an even split — coming from lineups rather than from tennis.

The advantage is real and smaller than the headline. Part of it is a logistics problem.

It is not that the strong teams are at home

The obvious objection is that the home column might just be collecting better teams. That is testable: take only the pairs who played each other once at each venue in the same season and fielded every line both times, so the same two teams sit on both sides of the comparison and strength cancels exactly.

Whatever is left is the venue. Of 893 pairs, home took 523 and the road 370.

Read this one carefully

58.6% is not the home advantage, and quoting it as one would overstate the finding. Requiring the pair to split selects for evenly matched opponents, which is exactly where a venue is able to decide anything. It is the effect among matches close enough for it to matter, which is why it is bigger than 55.8%. The honest headline is still the first number.

Season by season

2022: 56.1% · 2023: 55.7% · 2024: 55.4% · 2025: 55.4% · 2026: 56.3%

No season is an outlier, and whatever produces this is steady — a court somebody practises on, a drive somebody makes after work — which is what a cause built into the fixture looks like rather than a run of results.

So the belief is right, with a footnote nobody says out loud: part of the home team's edge is simply that the away team is the one arriving short.

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Grounded — every figure above is a count over a stated denominator. No estimates, no model output: just match results and what they add up to.

Scope. USTA NorCal adult league scorecards for Marin County and San Francisco, seasons 2022–2026. It is those two areas, not NorCal and not a national figure. 15,445 team matches had a decided result; 251 ended level and are excluded, because a tie has no winner.

What "home" means here. The label the source publishes on each scorecard. USTA NorCal league matches are played at the home team's facility, but nothing in this data records a venue — so what is measured is the label, and any explanation involving actual courts is inference rather than measurement.

What "a line went unfielded" means. A line on the scorecard where one side named no players at all. That is the clearest signal available for a defaulted line; it is not a judgement about any team, and no team or player is named anywhere on this page.

Method. Every figure above was produced by the SQL recorded in docs/research/records/home-advantage.json and re-run against the live database before this page was built. The record also carries what was checked and could not be removed. Reproduce with npx tsx scripts/measure-research-record.ts.