March Madness betting: Beware that if you bet favorites, the spreads are inflated



Generally, casual bettors like betting favorites. And March Madness brings in as many casual bettors as any event.

Given that, this won't surprise you much: For just about every game in the first round of the NCAA tournament, the point spreads at BetMGM have been inflated a bit toward the favorite.

Just about any college basketball fan by now understands that KenPom.com is a valuable resource and oddsmakers have taken to checking out the site too before posting lines. KenPom is the most popular projection site there is.

And in almost every single case for Thursday and Friday games at the NCAA tournament, the odds have been shaded toward the favorite. That means if you bet favorites, you'll be laying at least an extra half point in just about every bet, if you trust KenPom's projections.

An interesting trend in the odds
There are 28 first-round games with a point spread. There are no lines yet for the games that involve a First Four opponent. Let's eliminate the four games in which the KenPom favorite and the betting favorite differ (for the record, the four teams that are favored by KenPom but not at BetMGM: Boise State, Michigan, San Francisco, Loyola Chicago).

That leaves 24 games. And when comparing the KenPom projection and the BetMGM odds, the line was moved toward the favorite 23 times. The only game in which the line moved toward the underdog is San Diego State vs. Creighton. San Diego State is favored by 3 points at KenPom and just 2.5 points at BetMGM.

Among the other 23 games, the line only moved a half-point toward the favorite nine times. That might seem insignificant, but you've seen the NCAA tournament before. It's not that crazy to see a game finish within a half-point of the spread. It only takes one half-point loss on a big bet to understand how important the difference can be.

There are 14 games in which the betting line is shaded by more than a point, compared to KenPom. For one example, Duke is projected to beat Cal State Fullerton 79-65 at KenPom. But at BetMGM, Duke is favored by 18.5 points, not 14 like KenPom projects. Duke, of course, is a brand name and easy for casual bettors to take in the first round. They'll pay a tax for it.

Casual bettors like taking favorites
For most bettors who might just bet big events like the Super Bowl and March Madness, the difference in half points doesn't really matter. Regular bettors can obsess over those small edges.

KenPom isn't a betting site, but one that calculates efficiency per possession and comes up with a projected score for any matchup. There's more to analyzing games than following a strict mathematical equation. But this trend from oddsmakers is a bit telling.

What does it mean that oddsmakers have made the decision to shade 23 of 24 games toward the favorite? The most logical conclusion is that March Madness is a huge betting event, the public likes favorites, and maybe those extra half points mean some extra wins for the house. More than $3 billion is expected to be bet on the NCAA tournament this year, and even a few half-point wins has a huge impact on a sportsbook's bottom line. Over the last 10 tournaments the better seed (which is usually the favored team) is 145-167-7 (46.5%) against the spread in the first round, according to Matt Eisenberg's tournament guide. Underdogs usually do pretty well covering spreads in the first round of the tournament. One reason is the spreads are often shaded a bit against them. It adds up.

That information might not stop anyone from betting Duke if he or she believes the Blue Devils are about to blow out Cal State Fullerton, or taking any other favorite. Just understand you're likely laying a little bit extra on that favorite you like.

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