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Glenn Earl hits with ferocity, his impact as shattering as that of a toddler knocking over blocks.

But run into the Notre Dame free safety on the street and you will observe a friendliness that belies his aggressiveness, toughness and pure passion for hitting. Those traits, as much as anything else, have helped the Irish to a 9-1 record as they prepare to play host to Rutgers on Saturday.

Earl’s penchant for plowing through opponents has been part of his playing style even before the Lisle native played at Naperville North. His skills were developed under the watchful eye of his father, Glenn Sr., a former Indiana State football player who served as his son’s first coach.

“Pop Warner football, my dad coached me from when I was 6 years old until I was 13,” Earl said. “I definitely value his criticism and what he says.

“[Before every game,] he tells me to keep my head up and run though my tackles.”

Earl has done that for 65 tackles this season, good for second on the team behind linebacker Courtney Watson’s 81.

Moreover, Earl’s bone-jarring hits are the types that make someone think twice before getting up.

“He’s just one of those guys who loves contact,” Notre Dame cornerback Vontez Duff said.

“His eyes light up when he hits people,” defensive coordinator Kent Baer said. “He just has that toughness about him, and you love that, and that some day is probably going to make him a lot of money.”

Added strong safety Gerome Sapp: “We joke with him about that sometimes, he’d rather go for the hit than the ball.”

Earl didn’t make his first interception of the season until Oct. 26, in Notre Dame’s 34-24 victory over Florida State.

“That was a fluke,” Duff said. “It bounced off the ref and he grabbed it.”

But against Navy, Earl made what his secondary-mates are calling his first “legitimate” interception of the season. With 1 minute 32 seconds left in the game and the Irish leading by seven points, Earl intercepted quarterback Aaron Polanco.

“That was real,” Duff conceded. “He’s on the list now.”

Interceptions or not, Earl alters the tenor of every game.

“When we go into a game and they have great receivers, I talk to him about setting the tempo and tone early so that a guy can’t go over the middle, and he takes that to heart,” Baer said.

“I think I see some things that other people don’t see and in the course of the game I know what I did, what I did well, what I missed, what I didn’t do,” Earl said.

“He sees stuff. Everyone sees stuff like this,” Irish cornerback Shane Walton said, holding his hand upright. “And he sees stuff like this,” Walton added, pointing diagonally. “He just takes what coach said and dissects it to the smallest parts.”

Then, before every game, in late-night conversations with traveling roommate Sapp, he reconstructs those parts into a solid strategy.

Away from football, Earl said, “I just sit and watch TV. I’m probably the laziest person there is. I just do nothing to relax, I sit there and don’t perform any duties or activities.

“I’m really a mild-mannered person, kind of introverted,” he said. “But on the field you kind of have to let loose and flip the switch. Kind of like Dr. Jekyll and Mr. Hyde.”