For the second straight year, the Indianapolis Colts have made it past the season’s halfway point without a loss. Only three teams with winning records remain on their schedule, but Dallas may be the biggest obstacle between the Colts and a perfect season.

INDIANAPOLIS COLTS (9-0) AT DALLAS COWBOYS (5-4)
(Sunday, 4:15 p.m.)

By wins and losses, the Colts are far superior to the Cowboys, but a closer look shows two teams that aren’t that far apart. Football Outsiders’ Defense-adjusted Value Over Average ratings (DVOA) — which break down each play of the season and compare it to the NFL average based on situation and opponent — rank the Cowboys a surprising sixth, while the Colts are just one spot higher. The Colts may be undefeated, but only two of those wins have come by more than a touchdown, and they’ve had trouble pulling away from opponents both good and bad.

The Cowboys have two big factors in their favor. Dallas may not be Buffalo, but there’s a difference between playing in a dome and playing outside as the sun sets on a November afternoon. More important, the Cowboys are similar to two teams that beat the Colts last year, San Diego and Pittsburgh.

Start with the Cowboys’ 3–4 defensive scheme. The Colts offense is based on quarterback Peyton Manning adjusting plays at the line, and he historically has trouble against the 3–4 because the identity of the pass-rushers before the snap is hard to discern.

Fans may think that Indianapolis’s recent win over New England exposed Manning’s 3–4 problems as a myth, but that’s not the case. After adjusting for strength of schedule with DVOA, two of the three lowest-rated games for the Colts offense are the game in New England and the only other game against a 3–4 team, a last-minute victory over the Jets.

The Cowboys bring pressure with their linebackers, and DeMarcus Ware would love to rattle Manning just like past nemeses Joey Porter, Shawne Merriman, and Willie McGinest. The Colts do get a break now that linebacker Greg Ellis, second on the team in sacks, is out for the year with a torn Achilles.

Another popular strategy against the Colts is to leave defensive backs all back in coverage, shutting down long passes to Marvin Harrison and Reggie Wayne and forcing Manning to build drives around dink-and-dunk passes to open tight ends and running backs. This is the strategy that both Tennessee and Buffalo used in their near-upsets, the only two games this year where the Colts have scored less than 21 points.

Most fans, when they think of the Dallas pass defense, remember a series of long bombs in nationally televised games against Philadelphia and the Giants. Those plays make it hard to believe that the Cowboys could stop the Colts from throwing deep, no matter how many defensive backs are in coverage. But since the Cowboys sat rookie safety Pat Watkins, who was heavily responsible for those plays, the Cowboys’ pass defense has climbed from 29th to 18th in DVOA.

With defensive backs in coverage so often, Colts running back Joseph Addai usually sees just six or seven defenders in the box. The Colts are the best team in the league running up the middle or behind the guards, but Addai will often find nose tackle Jason Ferguson blocking his path. Overall, the Dallas defense allows just 3.5 yards a carry, third in the NFL.

The bad news for Dallas is that their biggest defensive weakness matches the popular strategy they are likely to play against the Colts. The Cowboys give up a lot of yards and first downs on passes to tight ends and running backs. Maybe he won’t hit Harrison for any 50-yard bombs, but Manning should have no problem slowly marching the Colts down the field with passes to Addai and tight ends Dallas Clark and Ben Utecht.

Therefore, it usually isn’t enough to slow the Colts; you have to outscore them. This is another place where Dallas fits the mold of teams that beat the Colts: a big-time running game, and a variety of weapons in the passing game.

The Dallas ground attack, led by the one-two punch of Julius Jones and Marion Barber, ranks fourth in the league in DVOA. The Cowboys have more runs from running backs than any other team — surprising, considering that teams usually pile up carries while closing out wins, and nine teams have won more games than the Cowboys.

Despite a slight improvement in recent weeks, the Colts still allow more than five yards a carry. Their chances of stopping Dallas get a lot better if safety Bob Sanders can play; after returning from a month-long injury, he made a huge impact against New England, then had to sit out again last week.

Using Sanders or another safety to stop the run leaves things open for the pass, and the Colts’ defense is below average there, too. The strength of the Colts defense is the pass rush. That would have been a great weapon against Drew Bledsoe, but the Cowboys replaced Bledsoe with Tony Romo specifically because of Romo’s ability to avoid mistakes under pressure.

The Colts often control the opponent’s best receiver, but give up big plays to other guys. Against the Colts, Jerricho Cotchery outgained Laveranues Coles, Eric Moulds outgained Andre Johnson, and David Kirkus outgained Javon Walker. Dallas has the best receiving corps in the league, and between Terrell Owens, Terry Glenn, Patrick Crayton, and Jason Witten, someone is bound to get open.

Expect a lot of offense, and a lot of long drives. The Colts are the only team in the league to convert more than half of their third-down opportunities, and the Cowboys rank second at 49%. Although the Dallas defense is above-average stopping third-down conversions, Indianapolis ranks 30th.

Dallas has all of the ingredients needed to upset the Colts: home field, a running game, a varied passing attack, and a 3–4 defense. Of course, New England had all these ingredients as well, and the Colts won anyway. Even if you can play the right cards against the Colts, sometimes Peyton Manning will just trump them all.

Mr. Schatz is the editor in chief of FootballOutsiders.com.