Which books run stale into the close

The question

Someone on r/sportsbetting said Fanatics usually had the worst MLB totals about six hours before first pitch, and asked whether it held up. Every book's price on every game is captured here about once an hour, so it was checkable. The short version is that the claim does not hold, and the book that does stand out is a different one entirely.

Method

For every game, market and book the study takes the price about six hours out, three hours out and one hour out, and compares each one two ways.

The first is against that same book's own closing price, which sounds like the obvious way to measure staleness. It turns out to be close to useless, and that is the most useful thing in the study.

The second is against the median of every other book quoting the same bet at that same moment. That is the one that answers the question, because it does not depend on whether the game later moved a lot or a little.

Everything is in probability points on the de-vigged price. On spreads and totals only prices sitting on the same number are compared, because Over 8.5 and Over 9.0 are different bets and comparing them just measures the half point. Since that leaves something out, the study reports separately how often each book's number itself moved, which is the other way a book can be slow.

The original claim

Fanatics came out at the bottom of the MLB totals table, not the top. Six hours out it sat 0.31 probability points from the field, the tightest of any book, across 290 games. The widest at that hour was BetPARX at 0.70, a little over twice Fanatics. Even that gap is modest, and most of the middle of the table is inside its own error bars. Whatever produced the original impression, it is not visible in a month of captured prices.

What does stand out is MLB moneylines, where Fliff sits 0.81 points from the field against 0.29 for the tightest books. The gap holds at three hours and at one hour and the intervals do not come close to overlapping.

Why measuring against a book's own close does not work

Comparing a book to its own closing price mostly measures how much the game moved, not how slow the book was. Every book faces the same market move, so they all score similarly. The variation between games is larger than the variation between books inside a game.

It is not a rare edge case. On MLB, a large share of book-samples are exactly the closing price to the cent, and that share rises steeply into first pitch. Every one of those scores a perfect zero on this metric.

It gets worse than uninformative. A book that never moves at all scores very well, because its price six hours out is nearly its closing price by definition. One pulled by hand from the July window: Red Sox at Athletics, home side. Six hours out Fliff had +135 while the other seventeen books were spread from +120 to +135, and it then held +135 for six straight hours into first pitch. Its distance from its own close was 0.4 points, which looks excellent. Its distance from the field was 2.1 points, which is the truth.

That example also makes the fairness point. +135 was the longest home price on the board, so on that game being furthest from the field meant the best available price, not the worst. Which direction a book is off in is a separate question, and it is the one the weakness map was built to answer.

Three books that are not really three books

Bally Bet and BetPARX posted the identical American price and the identical line on 99 percent of the snapshots where both were quoting. BetRivers matches those two about half the time. All three run on the same pricing platform, and it shows: their deviation figures are identical to two decimal places across every market and every time bucket. If you are shopping across those three, you are not really shopping.

The same check in reverse is a good sanity test. LowVig and BetOnline post different American prices most of the time, because one is the reduced-juice skin of the other, but after de-vigging their fair probabilities land a median 0.015 probability points apart. Same opinion, different margin.

Two different kinds of slow, on totals

Books split into two camps on MLB totals. One camp tracks the consensus number and re-prices: Pinnacle and Bovada moved their totals between six hours out and the close in about a third of games. The other camp parks on a number and stays there, theScore Bet and Hard Rock in under a fifth.

That sounds like the second camp is faster, but it is the opposite. Those same two books sit on a total different from the market consensus about 46 percent of the time, against roughly 9 percent for the books that re-price. They are not agreeing with the market quickly, they are sitting on their own number. For a bettor that is not automatically bad. A book still on 8.5 when the market has gone to 9 is offering a genuinely different bet, and sometimes the better one.

Caveats

The capture is hourly, not continuous, so a genuine intraday spike between captures is invisible. The close is the last stored price before the scheduled start, and book-games without a close within fifteen minutes of it are dropped entirely rather than given a stale stand-in.

Thirty days covers enough MLB games to separate the books at the top and bottom of these tables but not enough to rank the middle, where most of the intervals overlap. Two books 0.05 apart are not distinguishable here.

One structural quirk worth flagging: BetRivers shows a 21 percent line move rate on the MLB runline against single digits for everyone else. That is not slowness. It switches from the standard 1.5 runline to a 1.0 runline near the close, which is a different bet rather than a late move.

Nothing here says a wide book is a bad book. Distance from the field measures how much a book is doing its own thing, which is worth knowing before you decide where to shop, and no more than that.