One broken ankle changed everything. Denver is about to host an AFC Championship game as potentially the biggest home underdog in NFL conference championship history, and it's all because Jarrett Stidham is starting instead of Bo Nix.

The Quick Hit

• What happened: Bo Nix's season-ending ankle injury flipped the line from Broncos -1.5 to Patriots -5.5
• The damage: Seven-point swing based on one player
• Why you should care: Historic underdog value or complete trap?
• The move: If you believe in miracles, Denver +5.5 and +210 ML are sitting there

The Line Movement That Broke Brains

Before Nix went down in overtime of Denver's win over Buffalo, lookahead lines had the Broncos as 1.5-point home favorites against New England. Then the X-ray came back, and the books adjusted.

The line opened at Patriots -5.5 and has since settled at -5 at most shops, with some still showing -4.5. We covered the initial reaction earlier this week, but the situation keeps getting more unusual.

Jarrett Stidham will set the record for fewest career starts (four) of any starting quarterback in NFL conference championship history. The Broncos went from hosting a coin-flip game to being a touchdown underdog at home in the span of 24 hours.

What the History Books Show

Finding the biggest home underdog in conference championship history requires digging, but early indications suggest Denver could set or tie that mark. Home teams in these games are typically favored or getting points under a field goal.

The total also tells a story. Before the Nix injury, lookahead totals for this matchup were sitting at 45.5. Books adjusted it to 40.5 after the injury and opened the official number at 41.5. They're expecting a slugfest, not a shootout.

The Case for Denver

Sean Payton is still the coach. The Broncos defense is still elite. And Stidham only needs to be competent, not heroic, for Denver to stay competitive.

The +5.5 covers every one-score loss. If this game is 17-14 Patriots in the fourth quarter—entirely possible with two good defenses—the Broncos cover easily.

The Case Against

Stidham has thrown 25 career passes in meaningful games. He's going against a Patriots defense that just shut down Houston's high-powered offense. The moment might be too big.

The sharps have already pushed the line from -5.5 to -5 at some books, suggesting some professional money landed on Denver early. But that doesn't mean they think the Broncos will win—it means they think +5.5 was too much.

Sunday's Setup

AFC Championship: Patriots at Broncos, 3 PM ET on CBS

• Spread: Patriots -5 (was -5.5)
• Total: 41.5 (was 45.5 pre-injury)
• Moneyline: Patriots -255, Broncos +210

Check out our full Conference Championship preview for the NFC game between the Rams and Seahawks.

The Bottom Line

Denver being a five-point home underdog in a conference championship is absurd, but so is starting a quarterback with four career starts in this spot. Both things can be true.

If you're betting the Broncos, you're betting on Payton's coaching, the defense, and Stidham being able to manage the game. If you're betting the Patriots, you're betting that experience matters and Stidham will crumble under pressure.

Either way, this line is historic. We might never see a home team this big of an underdog in a conference title game again.