by Aaron Schatz

According to Football Outsiders stats, the top four teams in football all play in the AFC. Baltimore and Indianapolis present the ultimate matchup of strength against strength. In San Diego, the two most balanced teams in the league face off, but only one can move on.

For those who may be visiting this site for the first time to read this preview, we explain our stats at the bottom of the page, or click this link [1]. Each preview also includes a link to the game discussion thread for that game. We're doing separate game discussion threads for each game this year, rather than combining both games on the same day like we did last year.

Indianapolis at Baltimore

During the game, please join the discussion in the Colts-Ravens Game Discussion Thread [2].

Also of interest: This week's Every Play Counts on the Colts run defense [3] and last week's Too Deep Zone on how to run on the Colts [4]. Every Play Counts also covered the Baltimore linebackers [5] back in November, and you can also read the classic articles on Odgen vs. Freeney I [6] (2004 Week 15) and Ogden vs. Freeney II [7] (2005 Week 1).

This game will be promoted as the ultimate matchup of opposites: the best defense in the league, Baltimore, against the best offense in the league, Indianapolis. But not every portion of this game presents a matchup of opposites. The Baltimore offense is much improved over the second half of the year, and last week's outstanding performance against the Chiefs does not mean the Colts' defensive problems have suddenly disappeared.

WHEN THE COLTS HAVE THE BALL

Peyton Manning picked the Ravens apart when these teams played in the first week of the 2005 season, but the 2006 Ravens are far superior to last year's model and a worthy successor to the Super Bowl champions of 2000.

DVOA says Baltimore was the best defense in the league in nearly every area. They were first against the pass and second against the run. They ranked among the top three defenses on first, second, and third down. They were the best defense in the red zone and had the best pass rush as judged by adjusted sack rate.

As dominant as the Ravens were on defense, the Colts were even more dominant on offense. Their raw statistics were limited because so many teams slowed down the pace against the Colts defense. But the Colts had the second-best offensive DVOA of the decade, behind only their 2004 counterparts. They ranked first in passing and sixth in rushing. They had the best adjusted sack rate. They were second on first down, second on second down, and first on third down by an absurd margin.

The Colts converted 56 percent of third-down opportunities. No other team converted more than 50 percent -- in fact, only one other team converted more than 45 percent. Baltimore opponents, however, converted just 29 percent.

Each team has one weakness that can be exploited by the other. For the Ravens defense, that weakness is cornerback Samari Rolle. While Chris McAlister has been one of the best cornerbacks in the league this year, Rolle has been one of the worst. He doesn't give up a lot of big plays because the Ravens are putting so much pressure on the quarterback, but when the ball does get in the air, a receiver covered by Rolle tends to catch it and run a long way. And no quarterback does a better job than Peyton Manning when it comes to identifying a weakness in coverage and picking on it over and over.

For the Colts offense, the weakness is Manning's historical trouble against the 3-4 defensive. Manning's ability to change plays at the line depends on recognizing the pass rushers. That's harder to do against a 3-4 defense, and hardest of all against the Baltimore defense, which constantly shifts players around. Sometimes it is a 4-3, sometimes it is a 3-4. Linebacker Adalius Thomas might be a safety on one play, a defensive end on the next. Last year's playoff loss to Pittsburgh demonstrated the way the Indianapolis offensive line can be manhandled by fast pass-rushing outside linebackers -- like Baltimore's Bart Scott -- if Manning doesn't set up the protection perfectly.

WHEN THE RAVENS HAVE THE BALL

After six games, the 2006 Ravens looked the same as the Ravens of every other recent season: a great defense with an inept offense. But during the bye week, head coach Brian Billick fired offensive coordinator Jim Fassel and took over the playcalling duties -- and everything changed.

The Ravens ranked 26th in offensive DVOA after six games. Since their bye week, they rank eighth. Quarterback Steve McNair averaged 4.7 net yards per pass in the first six games of the year, and 6.9 net yards per pass since the bye week. Todd Heap is a great tight end, Mark Clayton a deep threat, and Derrick Mason a reliable possession receiver who has played with McNair for most of the last decade. The Ravens are also the only offense with a lower adjusted sack rate than Indianapolis [8].

Ironically, the one thing that hasn't improved much in Baltimore is that thing the Colts have such trouble with: the running game. The Colts allowed 5.3 yards per carry in the regular season, the worst figure in a decade. But Jamal Lewis hasn't been good since 2003, and he averaged a subpar 3.6 yards per carry this season. When McNair and the passing game got going, Lewis's average stayed exactly the same.

The Ravens run 67% of their carries up the middle or behind the guards, which makes their running game predictable. Last week, the Colts stuffed the line with defenders, knowing the Chiefs would want to run up the middle on them. It will be interesting to see if the Ravens can change their running philosophy and give the Colts something they won't expect, like counters and draws, plays that the Colts couldn't stop during the regular season.

Even if the Colts do manage to stuff the Ravens' running game and force third down, their biggest task is still ahead of them. The Ravens had a below-average offense on first and second down, but rank sixth overall on third down. They were particularly strong in midrange third downs, 4-6 yards to go. The Colts, meanwhile, ranked 30th in defense on third downs.

Selling out to stop the run leaves the Colts susceptible to the pass. Trent Green couldn't take advantage of it, but McNair will.

SPECIAL TEAMS

Both Adam Vinatieri and Matt Stover are excellent field goal kickers, and both are strong on kickoffs. But Baltimore is far better than Indianapolis when it comes to both kickoff coverage and kickoff returns. The two teams are fairly even on punts.

OUTLOOK

The Colts offense and Ravens defense will probably duel to a stalemate, making the other matchup the one that decides the game. Most people don't understand how good the Baltimore passing game has been over the second half of the season. The Colts may stop Jamal Lewis like they stopped Larry Johnson, but unless Steve McNair chokes, the Ravens should move on.

New England at San Diego

During the game, please join the discussion in the Patriots-Chargers Game Discussion Thread [9].

Also of interest: A November Every Play Counts on the San Diego offense [10] and this Any Given Sunday on New England's worst game of the year, the loss to Miami in Week 14 [11]. Also, Too Deep Zone articles on running [12] and passing [13] from multiple-tight end sets, which both the Patriots and Chargers use frequently.

We'll start this with the same announcement that has started every Patriots playoff preview I've written during the four years of Football Outsiders: I'm a Patriots fan. If you want to look for hints of bias in the preview, you are welcome to do so.

However, it is not my personal rooting interest that leads me to say that New England is just as good as San Diego. It's the numbers. This is not like last year, when the Patriots weren't even in the DVOA top ten [14] and Patriots fans were slightly deluded, counting on Bill Belichick's magic beans to hand-deliver them a third straight championship. The 2006 Patriots are one of the league's elite teams again. This team is not as good as the 2004 team [15] that won the Super Bowl, but it is as good as the 2003 team [16] that won the Super Bowl, and as good as the current Chargers.

These are the two both balanced teams in the league. Both can pass the ball and stop the pass. Both can run and stop the run (except in one important situation, as you'll see below). Both are good on special teams. The Patriots were a slightly better team over the second half of the season (higher weighted DVOA), but the Chargers were more consistent over the whole year (higher total DVOA and less variance). Home-field advantage and a week of rest makes San Diego the slight favorite, just as it makes New Orleans the slight favorite on Saturday night.

WHEN THE PATRIOTS HAVE THE BALL

If the Patriots beat the Chargers on Sunday, they can thank the New York Jets. The reason has to do with New York's midseason upset, not New England's first-round playoff victory.

Back in their Week 10 win, the Jets shut down the New England offense by blitzing Tom Brady relentlessly. In response, the Patriots altered their protection schemes, leaving more blockers and giving Brady more time to throw. That's key against San Diego's hellacious pass rush, particularly linebacker Shawne Merriman, who led the league with 17 sacks despite a four-game suspension. Left tackle Matt Light has not played as well this year as in seasons past, and the Patriots can't let him try to take on Merriman alone.

The Patriots receivers have been derided all year as a bunch of no-names, but if Brady has time to throw, he can usually find one of them open. Occasionally the Patriots will go deep, but most of their passing game consists of slowly marching down the field in chunks of seven or eight yards, augmented by handoffs to Corey Dillon and Laurence Maroney.

Watch for Brady to pick on cornerback Quentin Jammer; although he's the best-known name in the San Diego secondary, both Drayton Florence and Antonio Cromartie played far better this season [17].

A look at the numbers during Merriman's suspension shows just how important he is to the Chargers. With Merriman, San Diego was one of the top ten pass defenses. Without him, they were one of the ten worst. If we left out the four weeks without Merriman, San Diego's defense would be 10th in DVOA for the season and 12th in weighted DVOA.

Both of these teams are strong on first down: the Patriots offense is fifth in DVOA on first down, the Chargers defense eighth. The problem for San Diego comes on third down, where the Patriots rank third and the Chargers 18th. The Patriots were above-average on third down no matter how many yards were left to go, but the main issue here is third-and-short. The Patriots converted 82% of short-yardage situations, leading the NFL, while the Chargers stopped just 22% of these runs, which ranked 31st. Even a stop on third down won't necessarily stop a drive, since the Patriots converted 16 of 19 opportunities on fourth down.

These issues on third and fourth down are the sole reason why the Patriots' running game ranks so much higher than the San Diego run defense. If we only consider first and second down, New England's running game ranks 14th in DVOA and the San Diego run defense ranks 15th. On third and fourth down, New England's running game ranks second and the San Diego run defense ranks 30th.

The Chargers also need to keep the Patriots out of the red zone, where the Patriots offense is second in DVOA and the Chargers defense ranks dead last. It's more than just scoring touchdowns instead of field goals. Neither Brady nor the San Diego defense had any interceptions in the red zone.

WHEN THE CHARGERS HAVE THE BALL

Excited Patriots fans often dismiss the NFL's other teams as pretenders to the throne. But even the most obnoxious moron testing the limits of hubris on the WEEI Whiner Line has to acknowledge the greatness of the San Diego Chargers offense, led by MVP LaDainian Tomlinson and the best tight end in the league, Antonio Gates.

Young quarterbacks tend to struggle when they face a Bill Belichick defense for the first time, but Philip Rivers isn't your average young quarterback. In his first year as San Diego's starter, Rivers was one of the top quarterbacks in the league as well as one of the most consistent. That being said, his bad games were pretty much all in recent weeks, as he completed just 8 of 23 passes against Kansas City in Week 15 and just 10 of 30 against Seattle in Week 16.

Belichick will surely attack Rivers with hard-to-decipher blitz schemes, but the most important battle along the line will be one of the most simple. Left tackle Marcus McNeill enjoyed an outstanding rookie year, but it will be hard for him to handle Richard Seymour without some assistance.

The San Diego running game does the most damage on runs to the side, since both Tomlinson and his backup Michael Turner are spectacular once they get into space. Tomlinson's long touchdowns aside, the blocking up the middle is actually average. If the Patriots can somehow get the Chargers to run right up into the teeth of their all-first round defensive line, they can contain Tomlinson (contain here being a relative term).

The Chargers were number one in rushing yardage gained more than 10 yards past the line of scrimmage, but the Patriots don't allow a lot of long touchdown runs. The Patriots were number one in preventing such yardage for three straight seasons, and they were leading the league in preventing double-digit runs for the fourth straight season until two weeks ago. Maurice Jones-Drew's "not down by contact" 74-yard touchdown in Week 16 changed that statistic, but it's unlikely to be repeated by Tomlinson.

(Actually, New England's collapse in the "10+ Yards" stat is an interesting little story. Until Week 14, the Patriots had not given up a single run all year of more than 21 yards, but they gave up four such runs in the final four games. The first was 44 yards by Sammy Morris on the last non-kneel play of Miami's Week 14 shutout. Then came Jones-Drew. Add on a couple of long runs by Travis Henry in the final game of the year, and the Patriots dropped from first to 20th in this stat in two weeks. The first one was meaningless, the second one a fluke. It's those Henry runs that should worry defensive coordinator Dean Pees.)

The biggest area where Tomlinson can hurt New England is catching passes out of the backfield. That's a problem for the Patriots defense and an area where Tomlinson excels.

Like the Chargers, the Patriots have a strong starting cornerback, Asante Samuel, and a weak starting cornerback, Chad Scott. The Patriots often clamp down on the opposition's top receiver, only to allow a huge game to the number two option. For the Chargers, that could mean a big day for big second-year receiver Vincent Jackson. The idea of Scott or the diminutive Ellis Hobbs trying to cover Jackson or Antonio Gates is enough to make a famous fellow Patriots fan throw up in his own mouth while simultaneously setting himself on fire.

One more important note: both of these teams dial it up at the end of games. San Diego's offensive DVOA more than doubles in the fourth quarter -- while the Patriots' defensive DVOA more than triples.

SPECIAL TEAMS

The Patriots had the best kickoff returns in the league, and also excelled on punt returns, but San Diego was one of the top teams for both kickoffs and punts, making this a battle of strengths. Each team's main weakness on special teams matches up as well: the Patriots ranked 25th on punts, the Chargers 27th on punt returns. Nate Kaeding was a better field-goal kicker than Stephen Gostkowski this year, but the difference is a bit exaggerated because of Gostkowski's early struggles. In the first four weeks of the season, was the worst field-goal kicker in the league who didn't also punt. Since Week 5, including last week's wild card game, Gostkowski has been worth 2.3 points more than an average field-goal kicker in the same conditions.

OUTLOOK

If you can't enjoy a game between two teams with this much talent, you probably should avoid watching football for the rest of your life.

Stats Explained

DVOA (Defense-adjusted Value Over Average) breaks down each play of the season and compares it to the NFL average based on situation and opponent. You'll find it explained further here [18]. Since DVOA measures ability to score, a negative DVOA indicates a better defense and worse offense, and a positive DVOA indicates a better offense and worse defense.

Each team is listed with DVOA for offense and defense, total along with rush and pass, and rank among the 32 teams in parentheses. (If the DVOA values are difficult to understand, it is easy to just look at the ranks.) Red zone DVOA is also listed. These numbers are all regular season only.

WEI DVOA is WEIGHTED DVOA, which is based on a formula which drops the value of games early in the season to get a better idea of how teams are playing now (explained here [19]). This is the same formula used in this week's FOXSports.com power rankings, and it includes wild card games. All numbers except for WEIGHTED DVOA and the Stephen Gostkowski field goal thing are regular season only.

SPECIAL TEAMS numbers are different; they represent value in points of extra field position gained compared to NFL average. Field goal rating represents points scored compared to average kicker at same distances. All special teams numbers are adjusted by weather and altitude; the total is then translated into DVOA so it can be compared to offense and defense.

Each team also gets a chart showing their performance this year, game-by-game, according to total DVOA. In addition to a line showing each game, another line shows the team's trend for the season, using a third-power polynomial trendline. That's fancy talk for "the curve shifts direction once or twice." Note that even though the chart appears in the section for when each team has the ball, it represents total performance, not just offense.