Arizona Cardinals center Lyle Sendlein, who makes the calls for his team's blocking assignments, is expecting the biggest challenge of his career Sunday night during Super Bowl XLIII.
"I have to identify who is what and who is where," Sendlein said.
And when you're facing the Pittsburgh Steelers, that's often a problem.
Steelers defensive coordinator Dick LeBeau, inventor of the zone blitz, calls it the "fire zone." But it's really the vehicle that has driven Pittsburgh to the NFL's No. 1 defensive ranking for the past two seasons.
What is the fire zone?
•It's big on blitzing. Sometimes, the Steelers, who operate from a base 3-4 alignment, will bring up to seven pass-rushers.
•It's big on creating confusion. Defensive linemen sometimes drop into pass coverage. Safeties or cornerbacks might blitz, from the edge or up the middle. And the linebackers, the defense's strength, are the wild cards.
•It's big on responsibility. Linebacker James Farrior gets the call from LeBeau, then orchestrates the plan and aligns his players. The back side of the pass defense relies on zone coverage, sometimes similar to the "Cover Two" scheme popularized with the Bucs.
"The whole idea, the way it works, is to put a little doubt in that quarterback's mind," said Steelers assistant head coach John Mitchell, who works with the defensive line. "You want him thinking, 'How many guys are they bringing now?' You want it disguised well, so not only does he not know how many we're bringing, but he has no real idea where they're coming from?"
In this case, the quarterback is Kurt Warner, whose quick release and recognition ability basically sliced and diced Philadelphia's blitzing defense in the NFC Championship Game.
So there's a major key to this game: Can the Steelers provide the pressure before Warner pulls the trigger?
"They are going to throw things at us we've never seen before," Warner said. "I have to recognize what they're doing, where they're coming from, who we're blocking, who are the free guys."
The priority is accounting for linebackers James Harrison and LaMarr Woodley, the hybrid players big enough to be a lineman, but fast enough for coverage. Potentially, they are the players who could create the most damage.
"This year, I've covered receivers, I've covered tight ends and I've covered backs out of the backfield," Woodley said. "When you play defensive end as Woodley did at Michigan, you don't get any practice reps covering backs. So it's different, and there can be a little bit of a fear factor.
"Once you get over that, it's natural. It's what you do. With the pressure you can bring, there's not a lot of time with the coverage anyway. If things work the way we want, the quarterback is on his back."
Mitchell said it takes about three years for a player to be fully effective in Pittsburgh's defense. The scouts and coaches know what players to seek. Hybrid sizes are welcome. So are undersized defensive linemen. Cerebral safeties.
The common denominator: You must be able to run.
"The earth-mover defensive linemen types, the ones who just clog space, that's not what we're looking for," Mitchell said.
"We need guys who create some havoc."
Who is what? Who is where?
For the Cardinals, those are the questions. And their ability to determine answers - quickly - should determine the direction of Super Bowl XLIII.