The Super Bowl Betting Line Flipped Overnight. What Happened?

As soon as the N.F.L.’s conference championship games ended on Sunday night, bookmakers around the world announced their Super Bowl lines. Most installed the Kansas City Chiefs as the favorite over the Philadelphia Eagles, by about a point.

Gamblers disagreed. They thought the sports books had it wrong, and they pounced. Almost immediately, money began pouring in on Philadelphia, and pretty soon the line was on the move. Within an hour, the Eagles were the Super Bowl favorites. By Monday they were favored by 2 to 2.5 points.

What happened? And why did so many early bettors like Philadelphia?

The initial line should not have been a huge surprise. Most computer rankings have Kansas City a point or two better than Philadelphia. Oddsmakers who offered so-called look-ahead lines last week had suggested Kansas City — if it advanced — would be the Super Bowl favorite, by as much as 2.5 points.

But “the market flat-out disagreed,” said Brandon DuBreuil, the head of content at Covers, a sports betting information site.

The gamblers who bet early tend to be well respected, and are known as “sharp money.” When they all seem to like one team, bookmakers scramble to change the line.

And why did these sharp bettors all like Philadelphia? One key reason was injuries. Kansas City quarterback Patrick Mahomes has been dealing with an ankle sprain, and one of his favorite targets, tight end Travis Kelce, had been listed as questionable for the conference championship with back spasms. And even as the Chiefs won the game, 23-20, over the Cincinnati Bengals, they lost several wide receivers.

All those injuries will mean some uncertainty about the Kansas City offense before the Super Bowl, which will be played Feb. 12 in Glendale, Ariz. Another, perhaps more important, factor is how good Philadelphia looked.

While it is necessary to qualify the Eagles’ 31-7 win because the San Francisco 49ers were effectively left without a quarterback for most of the game, and while 2.5 points doesn’t sound like a huge spread in a title game, the revised line translates into a perceived advantage for the Eagles.

To bet on the money line — a straightforward wager on who will win the game — Philadelphia backers must bet $130 to win $100, while Kansas City supporters bet $100 to win $110. This translates into Philadelphia being given a 54 percent chance of winning the game against Kansas City’s 46 percent chance.

No opinion on the point spread? There are a lot of other ways to bet.

Depending on where you look, the over-under on the game is around 49.5, so bookmakers are looking for more scoring than in the A.F.C. (43 points) or N.F.C. (38 points) championship games, or indeed more than in any of the divisional round games (which produced a combined 31, 37, 45 and 47 points).

If you are impatient, you can bet over-under for the first half (24) or even the first quarter (10).

What’s next for the betting line? While there might be a little more movement, the major action is probably over. “I doubt the line will flip again, but it could creep down,” DuBreuil said, perhaps settling at something closer to Philadelphia by 1 or 1.5 points. The biggest moves of any line, he said, happen early.

Unless there is disastrous news, that is. If, say, it were announced that Mahomes would miss the game, a 7-point swing would not be a surprise, DuBreuil said. In that case, the Eagles might enter the game as much as a 10-point favorite.