CHICAGO — Here’s the skinny on how the Packers beat the Bears today to get to the Super Bowl: Fat stats by Aaron Rodgers, sure, but another key is the guy, once so thin he didn’t have a single athletic scholarship offer, who can climb under the skin of Jay Cutler.
Look at all 255 pounds of Clay Matthews now, after a 131⁄2-sack season on a bad leg, because of a motor that could drive him to NFC Defensive Player of the Year award in just his second season.
“He’s had a tremendous season, just tremendous,” Packers coach Mike McCarthy said.
In Green Bay, where Ray Nitschke roamed, they know tremendous, and the Bears of Bill George, Dick Butkus. Mike Singletary and now Brian Urlacher have had some linebackers, too.
“So much history,” Matthews said. “It’s only my second year, but I can take a big step [toward recognition] with a win this weekend.”
There’s going to be some good, old-time roaming and hitting today, the way a championship should be settled between the NFL’s two oldest rivals. So strap on your old leather helmet, old-timers, the kind Matthews figures Urlacher wore as a rookie.
“I can’t remember when I started remembering him,” Matthews said. “He’s still plays with that same energy and emotion, making plays I admire.
“Ten-plus years. It’s something special to play for a year or two.”
Matthews would know. As a junior at Agoura (Calif.) High, Matthews was 6-foot-1, 165 pounds, even thinner than his prospects of carrying on the family name in football.
Grandpa Clay played five years for the 49ers in the 1950s. Uncle Bruce made the Hall of Fame on the offensive line of the Oilers and Titans.
Dad, Clay Jr., who played the most games of any linebacker in history (Browns and Falcons), was the defensive coordinator at Agoura and was afraid to put his son on the field.
“His mom was giving me the business, but he wasn’t ready,” Clay Jr. said “He wasn’t very big and wasn’t very strong.”
It couldn’t have been easy being a Matthews and being no good. But even before Clay had hair running down to his shoulders, he still had a head on them.
“In all honesty, I wasn’t looking that far ahead,” he said. “When I wasn’t good enough my junior year, I just wanted to play as a senior, didn’t really see some big end in sight.”
Big-time schools, even little-time schools, saw the end as Grade 12. Not one offered a scholarship, so he walked on at USC, where his dad played.
“I thought I could come in on Day 1 and be the guy,” Matthews said. “Maybe I was crazy to have that mindset, but obviously that’s better than saying you can’t.”
He put on a red shirt for a season, made some special-teams plays the next, and earned a full ride. Though his hair grew outside his helmet, the media guide bio still ran the old crew-cut photo.
“Mom said I was more handsome than that and needed to take a new picture,” he said. “I liked it because it showed where I’ve come from: the skinny walk-on.”
Twenty-four NFL teams remained unimpressed enough to pass him over until the Packers took Matthews with the 26th draft pick in the 2009 draft, their second of the first round.
“He does give hope to a lot of guys because he wasn’t big enough and fast enough,” said Matthews’ college coach, Pete Carroll, now with the Seahawks. “Now, he’s perfect.”
So this is a chance his dad never had in 19 seasons.
“I’m a second-year player already in the NFC Championship Game,” Matthews said. “But this is truly an opportunity you shouldn’t squander.
“You don’t know when you’ll get back.”
jay.greenberg@nypost.com