When Houston Texans running back Arian Foster takes the ball behind the line of scrimmage, he's looking for an opening in the defense — even a small one — through which he can propel himself. With a cavalcade of rolling blockers in front of him, he usually finds it.

The NFL's 2010 rushing champion will be on the prowl again Sunday in Baltimore, but if the 2011 season is any indication, real estate at M&T Bank Stadium will come at a premium.

The Ravens haven't allowed a 100-yard rusher this season, and none since Foster did it last December. Their rush defense ranks second in the league, giving up just 72.5 yards per game and 3.2 per carry.

What's more, twice this young season the Ravens have been able to whip up the perfect storm. Against the Pittsburgh Steelers and New York Jets, they were able to get the early lead, stuff the run and win going away. Both teams gave up on the run early — out of necessity and futility — and became one-dimensional.

Foster, who punched out a quiet 100-yard game in an overtime loss to the Ravens last season en route to a 1,616-yard year, knows what to expect.

"They have their typical defense that they have had in the past," he said. "Very stout, very fast and they like to make big plays at big times of the game. I think with them, you just have to minimize your mistakes as much as possible and hope they make mistakes, and you have to capitalize when they do."

Asked this week about what makes Foster one of the league's best backs, the Ravens pointed to his vision, his burst of speed, his power and his scheme. Under coach Gary Kubiak, a former Denver assistant, the Texans operate a stretch zone running scheme which the Broncos first popularized and which the Ravens adopted this year.

"I think he just fits in that scheme really well," Ravens linebacker Jarret Johnson said. "They get you running and they wait for you to make a mistake. And he is awesome. Me and Ray [Lewis] talk about it every day: [when] Foster puts his foot on the ground [to cut], he's coming downhill. And there will be times when it looks like a defense is in good position, has every hole plugged and is playing with good leverage, and he just finds one slight, little crack. When he puts a foot on the ground, he's going to get 5 or 6 yards. It's impressive."

The stretch scheme allows the running back to pick his spot as the play unfolds before him. Houston runs it exceptionally well. The Texans have 11 100-yard rush games since the start of the 2010 season, most in the league in that time.

In the past six years under Kubiak, when the Texans run the ball 30 or more times, they are 26-3.

The Ravens, on the other hand, have allowed a league-low 18 rushing touchdowns and the third-fewest rush yards in the past four years.

In perhaps the day's most intriguing matchup, it will be the proverbial unstoppable force against the immovable object.

Foster rushed for just 68 yards in a Week 5 loss at Oakland, but had a career-high 116 receiving yards.

"He's a guy who gets the ball a lot of different ways," Ravens coach John Harbaugh said. "They get him the ball in screens … they give him the ball in quick flares. Our guys have to understand if he's releasing, he's releasing for a reason and it's usually to get him the football.

"He runs that stretch-zone scheme as well as anybody in football. He's a stretch-and-cut runner. [He has] great vision. Everywhere is the point of attack in that scheme."

What the Texans accomplish — and what makes the run game so good — is that they get defenders running laterally, and are able to knock them off balance, creating running lanes in the defensive front.

"They get guys running so fast," Johnson said. "And as you run, obviously you have to turn your shoulders. When you can't see [a defender's] numbers, it's not good defense. But in order to run with him, you have to turn. So you have to work on staying square, moving fast and when they cut [block], you've got to stay on your feet. Because when you get cut and you get a guy on the ground, that's where the ball's coming every time."

The Ravens say Foster, at 6 feet 1 and 227 pounds, will not go down on arm tackles, that he is quick enough to get past them and strong enough to run through them.

"As a front seven, we definitely have to hit him, hit him often and get him down as fast as we can." said defensive tackle Haloti Ngata.

Opponents have run the ball a mere 90 times against the Ravens. Only two teams, the Washington Redskins (78) and Dallas Cowboys (79), have faced fewer runs this season.

Terrence Cody, the Ravens' emerging nose tackle, can see the effect of the run defense in other ways, too.

"I see a lot of frustration," Cody said. "You could see that from the Jets. Not just the Jets, but … you could see that in the Tennessee game when they gave up on the run. You could see how Chris Johnson was getting frustrated when he couldn't get things going. I see a lot of frustration when people give up on the run."

If it happens again Sunday, it could mean another big win.

ken.murray@baltsun.com

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