The NFL season is now underway, but that means very different things for different teams. For some, this season is a path to the Super Bowl; for others, it’s a rebuilding year. But each week, all of these Davids and Goliaths have to show up and play – and the results aren’t always going to end up the way the stat guys say they will.

A lot goes into pulling off an upset: an outmatched team could get some lucky breaks, play a distracted opponent, or a win with a superior coaching strategy. Predicting an upset is hard to do with certainty, but we can sometimes tell when a weak team should have some hope – or when a good team should be extra careful. These are the teams that should be on upset alert during week one of the NFL season.

Indianapolis Colts (@ Buffalo Bills, Sunday at 1:00 PM)

The Indianapolis Colts are, with apologies to the New England Patriots and Denver Broncos, the class of the AFC this year. They have a great young quarterback, an easy division (and, frankly, conference), and all the optimism in the world. But the Buffalo Bills have a great defense that could get even better under new head coach Rex Ryan. If the Bills D can frustrate QB Andrew Luck in an outdoor game in Buffalo, this could be the first big upset of the year.

Green Bay Packers (@ Chicago Bears, Sunday at 1:00 PM)

On paper, this one is a no-brainer. You have the Green Bay Packers, who are a near lock to win the division and have the second-best Super Bowl betting odds in the entire league, versus the Chicago Bears, who may very well finish dead last in the division. But there are a few reasons for Bears fans to hold onto their pipe dreams at least through week one. The Packers will be playing without their deep threat, Jordy Nelson; they’ll be in Chicago, and NFL rivalry games often end up a lot closer than their mismatched rosters might indicate (looking at you, Patriots and Jets).

Denver Broncos (vs. Baltimore Ravens, 4:25 PM)

The Broncos have been a great team for several seasons, so it only makes sense that they’re favored in this matchup in Denver. Still, the Baltimore Ravens seem poised to put together a playoff-caliber season while the Broncos, with an aging quarterback learning a new offensive system, could be on the verge of taking a step back. This is one potential first-week upset that could look a bit less like an upset by the end of the season.

Philadelphia Eagles (@ Atlanta Falcons, Monday at 7:10 PM)

The Philadelphia Eagles are a very different squad than they were last year, but they’re a team that a lot of experts are picking to steal the NFC East from the Dallas Cowboys. In week one, they’ll get to start with a Falcons team that was woeful last year. Not so fast, though - the Atlanta Falcons, too, have made some offseason changes. And if the new coaching staff can make better use of QB Matt Ryan, or if the Eagles’ new-look roster takes a game or two to gel, then the results of this week one matchup could be surprising.