It's all based on power ratings. They don't change quickly, certainly not nearly as rapidly as public perception.
In fact, this number is actually a bit inflated based on every set of power ratings I've looked at. Most have the Dolphins somewhere in the neighborhood of 4.5 to 5 points above Denver, which would made the spread below a field goal. But the oddsmakers realize that public perception and even wise guy perception is toward a developing gap between these two teams, which is why the number opened slightly higher than power ratings would suggest.
There was late money on Miami yesterday, shoving the number from -1.5 to -2.5. There has been late money on the Dolphins many times this season and it has collected more often than not. Trust me, oddsmakers pay attention to that type of thing exponentially more than anything regarding football fundamentals. There has already been money on the Dolphins in this game, with joints now at -3 -120 or -3.5.
Somebody mentioned lack of running game in this thread, toward explanation of a low spread. You could sit through oddsmaker discussion of 1000 games and never hear anything about a running game. They don't care about technical football at all. It's 4-6 guys sitting around with the same sets of power ratings, and discussing where to open the new numbers, based on those power ratings, the home field adjustment (if any) and where they expect the money to go. The chief oddsmaker listens to everybody and then has final say.
It's too bad the weekly Las Vegas Seven went out of business a few years ago. They had a great article based on an actual oddsmaker session, of NCAA tournament games. That article was also online and included pictures of the session plus the dialog as a game was dissected and the line set. It is the only time I have ever seen the process depicted accurately. It is nothing like the public prefers to believe. Games are finished in 30 to 60 seconds tops. Nothing complicated at all. You'll almost never hear the name of a player or coach. In particular I used to link that article on a Canes site where the user base is nothing but Simplistic Angry Males who refused to believe the lines were based on power ratings. Unfortunately the print edition of Las Vegas Seven ended in 2017 and the online content was removed not much later.
Before I forget, here is the Jeff Sagarin NFL power ratings. He has the Dolphins roughly 4.5 points higher, at 22.00 to Denver at 17.53:
Keep in mind the oddsmakers and professional bettors are swamped. They are dealing with multiple sports and hundreds of games and props. I am not wagering as much as previously but right now I am still mentally exhausted from 25+ Masters wagers. I mention this only because fans on a specialized site like this are fixated on one point spread...Dolphins at Broncos. But the guys hanging the numbers only care about applying the same math-based formula all year long, and relying on the 11/10 advantage to grind a decent house take. That's why it has to be quick and subjectivity free.
Professional bettors likewise will view the game as one among many. If the Dolphins win 30-10 and you tell them Miami -3 was the greatest bet of all time and the stupidest line you've ever seen, they'll smile and recommend you don't do this full time. An upstart team on a 5-game winning streak and now road favorite is just the type of thing situational bettors like to oppose. Many sharp guys will wager on Denver for that reason alone. Some of them won't know who Drew Lock is. I'm not saying I would go that way. But I was in that environment for nearly 25 years. Situational analysis dominates the mindset of that type, just like fandom and technical football dominates on sites like this. They won't see this game as Miami at Denver, with all the related particulars. It will be viewed as a team that was supposed to win 6 games in 2020 and now has 6 already, including 5 in a row. Okay, time for some regression to the mean. If they are wrong they'll apply the same thinking and same wager the next time.
I won't have a wager on this game. Most of my underdog angles involve taking the road team. I would have had Chargers yesterday if that game had ever reached +4. Fortunately it did not. Same with this game. I would have Denver plus the points if the game were at Miami.
BTW, one of the reasons the Chargers line was so low is that they were 2-6. That was a popular angle throughout my years in Las Vegas...bet on NFL road underdogs during the second half of the season if their winning percentage is 25% or lower. It has an excellent history so guys play every one. But obviously you have to be able to stomach some dreadful teams and know you'll get hammered from time to time.
