No. 15 Iowa has perhaps the nation's best defense, a unit led by a ferocious front four and an opportunistic secondary.

Michigan has perhaps the nation's best offensive weapon in quarterback Denard Robinson, who's barely been slowed by anyone this season.

Whatever team gets the best of that matchup this weekend in Ann Arbor will probably walk away with a win.

Simple as that.

Iowa (4-1, 1-0 Big Ten) and its stingy defense — a nation's best 10.2 points allowed per game — will face its toughest test yet when they visit Robinson and Michigan (5-1, 1-1) on Saturday.

Robinson, nicknamed "Shoelace" because he prefers Velcro straps to lacing up, has blossomed into the ultimate dual-threat quarterback. He's rushed for 991 yards — more than double that of Iowa's leading rusher, back Adam Robinson — and thrown for 1,223 yards so far this season.

"You may think he's going to run it, and all of a sudden he pulls up and throws it down the field," Iowa coach Kirk Ferentz said. "If you wait for him to get across the line, he's not easy to catch. So he's got great speed, and he's proven to be very durable as well. It just puts a lot of pressure on you."

Iowa has held four of its five opponents to seven points or less, and its last two opponents, Ball State and Penn State, combined for a single field goal.

Iowa's numbers are even more impressive if the interception and kickoff returns taken back for touchdowns by Arizona in a 34-27 win over Iowa last month are taken out. The Hawkeyes defense has allowed just 37 points all season, and they're the only unit in the country that hasn't yet allowed a rushing touchdown.

Iowa's defensive line is led by stars Adrian Clayborn, Christian Ballard and the emerging Mike Daniels. The Hawkeyes also have a pair of All-Big Ten safeties in Tyler Sash and Brett Greenwood, who've excelled at picking off errant balls.

Iowa likely won't change much of what they do to stop Robinson.

"Their front four is as good as anybody's in the country," Michigan coach Rich Rodriguez said. "They're so good up front that they can get pressure with a four-man front. They can stop the run with their four-man front and playing their base defense against just about anybody. They don't stay blocked.

"They're a team that, you know, you may put a hat on a hat, but that hat on a hat doesn't stay there very long because they get off blocked."

Of course, avoiding all the hats is Robinson's specialty. He's second in the nation in rushing and total offense, and he's scored nine touchdowns on the ground in five games.

Last week, Michigan State limited Robinson to a season-low 86 yards on 21 carries. He threw for 215 yards, but also had three interceptions and was just 6 of 14 passing in the second half.

"We had a few dropped passes and Denard had a few missed reads. And those are the type of things if you do that in a tight ball game against a good opponent, they'll come back to get you," Rodriguez said.

Iowa has also seen Robinson before. The Wolverines brought him in during the second half last season at Kinnick Stadium. Robinson led them on a touchdown drive he also threw a pick with 46 seconds that sealed a 30-28 loss to the Hawkeyes.

Iowa focused more on Robinson's running ability than his arm in 2009 and it worked. This year, though, Robinson has proven to be a much more complete player.

Ferentz was asked if the Hawkeyes had anyone on their roster who could at least replicate some of the things Robinson does in practice. Ferentz interrupted with a simple no.

"If we had someone like that we'd probably be running that same offense," Ferentz said.