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NBA playoff betting: What's up with the big swing in the line for Celtics-Heat Game 4?

Issac Baldizon / National Basketball Association / Getty

Maybe it's not the NBA's dream championship matchup, but we're one game away from the completion of a perfect conference finals based on our betting preview last week. It goes to show that, with an understanding of how betting markets work, you don't need to know the intricacies of a sport - you don't have to pore over in-game lineup maneuvering or defensive effectiveness against 1-5 ball screens, etc.

Instead, if you're patient and allow the market to show you what it thinks of each team, you can tune in for the playoffs and let the action shape your view.

Whether it's grabbing the Nuggets (+800) as the fourth choice on the oddsboard before the postseason, or planting a flag in the Lakers as overrated before Game 1 of the Western Conference finals, knowing how the market feels about each team can be more important than how you feel.

What's going on with these Celtics-Heat point spreads?

Before the series started, the market told us the Heat were 8-point underdogs in Game 1 in Boston. Using our formula to help simplify things and assign values to each team out of 100, we were being told that Miami was considered around 60/100 with Boston close to 80/100. Miami's number was up from early in the playoffs when the Heat were considered barely above average - as a play-in team usually should be - before they consistently covered against the Bucks and Knicks.

If you think any team should be rated higher than the market's rated it, you should probably bet on that team. That's why we're holding Heat series tickets at +400 (or better) with one game to go and don't have to do anything with Game 4. Since the bigger point of all of this is to understand how point spreads work, however, let's dig into how the Celtics went from closing as 4.5-point favorites in Game 3 to current 1.5-point underdogs for Tuesday night.

The hypothesis is that the Celtics were -8 in Game 1 due to a 79-61 rating disparity and then docked a half-point for Miami's rest advantage. In Game 2, the consideration for rest was removed, and the Celtics got a point's worth of credit on the assumption they'd be desperate to avoid losing both games in Boston. As a result, the line closed Celtics -9.5 in Game 2.

Flipping Boston's home-court advantage of four points and 3.5 points for Miami's would have made Boston -2 for Game 3. Perhaps the Celtics closed as 4.5-point favorites because of the ill-fated idea that Boston had another 2.5 points of desperation in it.

It's easy with hindsight, but being able to guess the market's thinking should have led you to an easy bet (and even easier win) on the Heat +4.5, since 2.5-3.5 points on a narrative-based shift in the spread is ridiculous.

As it pertains to Game 4, we already know that Celtics -4.5 was wrong, but what would have been the right line from a market perspective?

Using pre-series ratings, Celtics -1 makes sense for games in Miami before accounting for our tongue-in-cheek oddsmaker adjustments. The zig-zag tax was heartily applied in Game 3, but now we might need to factor in the "one-two-three Cancun!" tax with the Celtics down 0-3 and the prevailing narrative stating that they've quit.

Celtics @ Heat (-1.5, 216.5)

With the Heat -1.5-point favorites, are we supposed to presume that not only have 3.5 points worth of Celtics' desperation gone away, but the market's gone 2.5 points further (through PK) because Boston's packed it in? That's just as narrative-based as the move we should have faded in Game 3.

What if none of the narratives existed? Relying purely on ratings, it's possible the Heat have continued to rise, going from the low 60s to the low 70s. We won't have a better idea about that until the NBA Finals when we should get to see how the market treats a Nuggets-Heat matchup, as Denver's rating has remained static.

As for Tuesday night's anticlimactic game - after a Game 3 that should have probably been a pick'em - Game 4 is a virtual coin flip. A bet on Miami is a bet on the idea that its rating still isn't high enough and/or the Celtics are ready for vacation. Meanwhile, a bet on Boston is predicated on the quitting narrative being nonsense and/or doubt that the Heat deserve so much credit.

Luckily, those who played the Heat for the series don't have to worry about it and can quietly wait for Miami to put Celtics fans and backers out of their misery.

Matt Russell is the lead betting analyst for theScore. If there's a bad beat to be had, Matt will find it. Find him on Twitter @mrussauthentic.

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