Patrick Mahomes is worth eight points to the betting public

Since Kansas City Chiefs quarterback Patrick Mahomes sustained a dislocated kneecap during the team’s 30-6 victory over the Denver Broncos on Thursday night — which will keep the league’s reigning MVP off the field for at last two weeks, and perhaps as many as five — perceptions about the Chiefs in 2019 have changed dramatically.

Among Chiefs fans, confidence in the team had already taken a severe hit after consecutive home losses to the Indianapolis Colts and Houston Texans. After being as high as 98% during Week 2 and Week 3, SBNation’s weekly FanPulse survey showed fan confidence in the team had dropped to 37% before Thursday night’s game.

But with a significant injury to the player who is clearly the face of the franchise, national perceptions about the Chiefs have also changed — as indicated by a tweet from friend-of-the-site Matt Derrick of Chiefs Digest on Sunday night.

Here’s the usual reminder about betting odds: they don’t tell you which team is most likely to win a game, but rather which team the betting public thinks is more likely to win the game. The whole purpose of betting odds is to get the same amount of money bet on both teams; when that occurs, the house is guaranteed to make a profit. So expert bookmakers set the initial line to attract more money to be bet for the team less likely to win. Then, as bets are placed, the betting line moves one way or another — eventually reaching a point of equilibrium that represents the betting public’s opinion about the game.

As Derrick noted, Mahomes’ injury caused one bookmaker to install the Green Bay Packers as initial three-point favorites in their road game against the Chiefs in this week’s edition of Sunday Night Football, saying that if Mahomes were under center, the Chiefs would have been favored by five.

That’s consistent with the way other oddsmakers see the upcoming game. In an article published Friday morning, SportsLine.com writer Matt Severance said the difference between the Chiefs with Mahomes and the Chiefs without Mahomes was nine points. At the time, it was unknown whether Mahomes would return before the end of the season. Severance said that if he didn’t, it would be bad news for the team’s prospects.

Just for informational purposes, SportsLine’s Projection Model would drop Kansas City’s win total from 10.0 to 7.7 were Mahomes to miss the rest of the season. The Chiefs’ chances to win the AFC West would drop from 75.3 percent to 27.3, their chances to make the playoffs from 81.4 to 31.7, to win the conference from 13.5 to 1.1 and to win the Super Bowl 7.0 percent to 1.1.

But is that an accurate representation of Mahomes’ effect on the team?

This season, the stats geeks at FiveThirtyEight.com made an experimental change to their Elo model of rating NFL teams, which calculates the probabilities each team will win every game in the NFL season. The change made this season is meant to account for the quality of the starting quarterback for each team. Unsurprisingly, Mahomes has the highest added value of any quarterback in the league; his backup Matt Moore has a value pretty close to average.

When accounting for Moore starting on Sunday night against the Packers’ Aaron Rodgers, the Elo model pretty much agrees with the bookmakers, saying Green Bay should be a 5.5 point favorite — compared to the Chiefs being favored by 2.5 under the traditional Elo model. In fact, the quarterback-adjusted model predicts the Chiefs would be 3-point underdogs against the Minnesota Vikings the following week and 1.5-point ‘dogs against the Tennessee Titans in Week 10. The Chiefs, however, would be favored by six points against the Los Angeles Chargers in Mexico City.

Based on the fact that difference in point spreads between the quarterback-adjusted and traditional Elo models steadily narrows to less than half a point by the time the Chargers game arrives in Week 11, it appears the FiveThirtyEight calculations are based on the expectation that Mahomes will return sometime before then.

Still, it confirms what we already know: Patrick Mahomes’ presence on the field is a significant part of the Chiefs offense. While losses in these next three games are far from foregone conclusions, Chiefs victories will likely require above-expectation performances not only from Matt Moore, but from the Chiefs defense, too.