Upset Watch: NFL Week 13

— -- Upset Watch appears every Thursday for ESPN Insider, as Football Outsiders uses a proprietary formula to forecast the expected point spread of each game based on current DVOA ratings ( explained here) and, early in the season, our DVOA projections. Each week we highlight the most likely upset on a game with a line over three points, plus an additional game where a significant underdog has a strong chance to cover.

Last week, we noted that Week 12 was a slate of very close games. This week, instead, we have a slate of extremely accurate point spreads. The formula we use to project point spreads at Football Outsiders comes up with a spread within one point of the actual spread for 10 of this week's 16 games, which is unheard of. That makes picking an upset of the week nearly impossible, but here are the most likely candidates (three-point spread or greater):

• Arizona (+3.5) at Philadelphia
• Atlanta (+3.5) vs. Buffalo (in Toronto)
• Kansas City (+4) vs. Denver
• Pittsburgh (+3) at Baltimore
• Tennessee (+4.5) at Indianapolis

For this week's Upset Watch, we'll go with a divisional rivalry that almost always results in close games, and this week gets a nationally televised holiday showcase. It could even decide the sixth playoff spot in the AFC.

Upset Watch: Pittsburgh (+3) at Baltimore

It sure seems like Pittsburgh and Baltimore always play games that are decided by three points, doesn't it? Actually, that's not hyperbole; it's really true. Nine of the past 13 games between Pittsburgh and Baltimore have been decided by only three points, and only one of them has been decided by more than 10 points. Those three-point games include a 19-16 Steelers win in Pittsburgh back in Week 7.

One of the driving storylines of this game is that these are two old-school running-and-defense teams that have been awful running the ball this year; the game is likely to be won by whichever team will just give up on the run and put the game in the hands of its quarterback. The Ravens rank 31st in rushing DVOA, ahead of only Jacksonville. The Steelers are just ahead of them at 30th, although they have been better (19th) since Le'Veon Bell played his first game in Week 4. Unfortunately for the Steelers, they are best running the ball to the right, where guard David DeCastro has been strong in his second year, but the Ravens' run defense is strongest against runs to the right.

Pittsburgh has particularly struggled running the ball on first down, and that includes Bell, who averages just 3.5 yards per carry on first downs. But when the Steelers put the ball in the air, they have a huge advantage on first downs. Only San Diego has a higher passing DVOA on first down, and the Baltimore defense is an awful 27th against the pass on first down. Big passing gains on first down are important because the Ravens have the advantage on second and third down. The Ravens actually have the best defense in the league on second down while the Steelers' offense ranks 11th. On third down, the Ravens' defense is 11th and the Steelers' offense is 24th.

One interesting aspect of the Week 7 game is that Ben Roethlisberger didn't throw a single pass to a wide receiver on the left side of the field, even though that's the side generally manned by Jimmy Smith, the weaker of Baltimore's two starting cornerbacks. (There is one pass listed in the play-by-play as thrown to Antonio Brown, but it was actually an intentional throwaway.) Over the course of the year, Baltimore has allowed 7.8 yards per pass on passes to wide receivers on the left side of the field, and just 5.7 yards per pass on passes to wide receivers on the right, so this seems to be a place where the Steelers could gain an advantage by changing up their strategy from Week 7.

The Steelers' offense does have to solve two problems in order to overcome the Ravens. First, Pittsburgh needs to leave in extra blockers to protect Roethlisberger. The Ravens rank third in adjusted sack rate (sacks and intentional grounding calls per pass play, adjusted for situation and opponent) while the Steelers' offensive line is just 26th.

The Steelers are also going to need to figure out how to punch the ball in when they get close to the goal line. The Steelers are a dismal 27th in offensive DVOA in the red zone, while the Ravens' defense is third in the league.

As for the Steelers, the most important thing they can do is leave safeties back to guard against the deep pass. Looking at Football Outsiders' receiving ratings, you can see that deep threats Torrey Smith and Jacoby Jones have both had very good years, while all the Baltimore tight ends and running backs have been below replacement level as receivers. Between the Ravens' ability to go deep and their inability to run, this is one game where Troy Polamalu is probably best used far away from the box.

Cover Watch: St. Louis (+9) at San Francisco

With the Rams and Cardinals both on hot streaks, Football Outsiders now ranks all four NFC West teams among the league's top 14 squads. The Rams are no longer the easy pushover they looked like a few weeks ago, and while the 49ers are clear favorites in this game, there's a good chance these teams end the game separated by a touchdown or less.

One of the problems for the 49ers has been an unwillingness to adjust their offense to put the ball in the air more often, and they'll need to do that if they want to beat St. Louis by more than just a couple of points. It may seem like Colin Kaepernick has struggled through the air, but actually the 49ers' offense is more efficient passing the ball (seventh in DVOA) than running it (11th). And because the 49ers run so much more than they pass, and running is generally not as efficient as passing overall, they actually rank 15th in offensive DVOA. In other words, the whole is less than the sum of the parts. This is the perfect week to get the ball in the air more, both because Michael Crabtree will finally be back on the field and because the Rams' defense is stronger against the run (ninth) than the pass (17th).

However, the weapon of choice shouldn't be Vernon Davis, because the Rams are fifth in DVOA against opposing tight ends, allowing only 40.9 yards per game. Instead, Kaepernick should look for Anquan Boldin, as the Rams are 31st against No. 1 receivers.