When the Market Moves 15¢ on a Favorite, What Actually Happens?

Since 2026-06-11 we've captured an opening and closing board for every MLB game we could. In 169 of them, through 2026-08-29, the closing favorite's price moved at least fifteen cents between the two.

Those 169 games are the study. Every row is published below — date, matchup, open, close, move, final score, and whether the favorite won. Nothing is filtered out after the fact.

The headline result is straightforward. What it means is considerably less so, and that second part is most of what this article is about.

The headline numbers

At a glance that reads like a finding: big moves on a favorite, favorite wins about two-thirds of the time. It's the kind of number that gets screenshotted.

It shouldn't be. Read carefully, that line says almost nothing — and understanding why is more useful than the number itself.

Favorites are favorites

Here's the problem with a two-thirds win rate for favorites: favorites are supposed to win about that often. That's what the word means.

A team priced at -180 is being sold as roughly a 64% shot. If a basket of such teams wins 65% of the time, the market was right, not wrong — and the study has discovered that sportsbooks can price baseball games, which was never in doubt.

The only question worth asking is whether these favorites beat their own prices. So we checked.

Now the two groups stop looking alike. The favorites the market walked away from closed at an average implied 58.6% and won 68.1% of the time — a gap of 9.5 points. The favorites the market moved toward closed at 64.0% and won 65.6%, a gap of 1.6.

In other words: the group the market grew less confident in outperformed its price by roughly six times as much as the group it grew more confident in.

If anything in this data is interesting, it's that cell. Not the headline.

Why we're not claiming that means anything yet

Because it still might not. Not at this sample size.

With 169 games and a true rate somewhere around 60%, the standard error on a win percentage is about 3.8 points. A 95% confidence interval spans roughly ±7.4 points. An observed 66.3% sits inside the range you'd expect from a market pricing these games correctly and getting a normal run of luck.

The "moved away from the favorite" group is thinner still: 47 games. The interval on that one is wide enough to drive a truck through.

Does the size of the move matter?

The natural follow-up: maybe fifteen cents is too low a bar, and the big moves carry the signal. Here's the sample sliced by magnitude.

There's no clean monotonic story here — the middle buckets outperform both the smallest and the largest, which is what noise looks like rather than what a mechanism looks like. Median move across the whole sample was 19¢; the largest was 63¢.

Two games that show the shape of it

August 19, Giants at Guardians. Cleveland went -210 to -225, all nineteen tracked books moving the same direction — as unanimous as this feed gets. Cleveland lost 1–0.

August 21: Philadelphia went -212 to -275, the largest move in the sample at 63¢. Philadelphia won 7–6.

Both are in the table below. Neither proves anything. That's the point of publishing all 169 rather than the two that make the best story.

How the sample was built

• Window: 2026-06-11 through 2026-08-29, every MLB game where we captured both an opening and a closing board.
• Qualifying: the closing favorite's consensus price moved 15¢ or more, in either direction, between those two boards.
• Consensus: median across every tracked book at that snapshot — typically 15 to 19 US books, not a single book's number.
• Open: the first board we captured that day, around 06:15 Pacific. Not necessarily the first number a book ever posted.
• Excluded: games priced beyond ±500, and games with malformed prices — typically suspended or resumed games being priced mid-score, which aren't line moves in any meaningful sense.
• Results: MLB official final scores.

All 169 games

The complete sample, unfiltered, in date order. Sort it, copy it, check it against your own records — that's what it's here for.

What to take from it

Three things, in order of confidence:

1. A big line move on a favorite is not, by itself, a reason to bet that favorite. The price already moved. Whatever the market learned is in the number you'd be paying.
2. The comparison that matters is against price, not against 50%. Any study that reports a win rate for favorites without reporting what those favorites were priced at has told you nothing.
3. 169 games is a headline, not a conclusion. We re-run this as the sample grows and republish it with the full table every time. When it says something, it'll say it with a sample behind it.