Don’t let Sean McGrew’s diminutive frame fool you. UW’s junior running back packs a punch.

Sean McGrew’s game doesn’t fit into his frame.

Look at him: he’s 5-foot-7, 186 pounds, fully capable of disappearing completely behind his hefty Husky offensive line. He’s a maple tree hidden by a row of massive redwoods. For comparison’s sake, he’s barely half of 347-pound freshman defensive tackle Sama Paama.

It would be natural, then, to conclude that he must be a slot receiver, or a silky returner, or a speed back determined to explode around the edge.

And yet …

“He’s probably one of the most physical backs that we’ve ever had at Bosco, in spite of his frame and stature,” St. John Bosco coach Jason Negro told The Times on Tuesday. “He’s kind of a compact guy, so he’s a little bit deceiving. I know he’s short, but Maurice Jones-Drew was kind of a short guy, too.

“But with the compactness that he has and his low center of gravity, you really don’t get a lot of good licks on him. I think that’s what’s made him so durable throughout his career.”

And what a career it was. In a prolific four-year prep run at St. John Bosco, McGrew amassed 5,762 rushing yards, 9.1 yards per carry and 85 total touchdowns. But Negro doesn’t particularly care about the numbers. He wants to tell you about the 2013 state title win over De La Salle, when the undersized sophomore carried 24 whopping times for 148 yards, despite the fact that “he basically got suplexed twice by Kahlil McKenzie.” At the time, McKenzie was 6-3 and 339 pounds of merciless, punishing muscle; the future Tennessee Volunteer and current Seattle Seahawk was a five-star defensive tackle and the No. 3 player in the country, according to 247Sports.

More than once, McKenzie picked up McGrew and threw him like a shot put. But the kid kept right on coming.

“The game Sean played that night was just remarkable,” Negro said. “He took a pounding, but as a sophomore, it was like his coming-out party. He was pretty special.”

Or, what about the comeback earlier that season against Chandler High? Bosco’s starting quarterback — who we’ll reveal in a little bit — was knocked out early with an injury, and Negro says “we had to start relying heavily on this skinny little tiny running back that was only a sophomore.” The Braves entered the locker room at halftime with a 28-17 deficit.

McGrew finished with 12 carries for 156 yards and a touchdown, and Bosco outscored Chandler — even without a certain unnamed signal caller — 35-3 in the second half.

“He was probably the most important guy (for our offense during his career),” Negro said. “And that’s pretty high praise, considering Josh Rosen was our quarterback during the time Sean was there.”

All of this goes to show that nothing you’ve seen this September should be particularly surprising. Yes, McGrew has compiled 204 rushing yards and a touchdown, averaging 6.2 yards per carry, through the Huskies’ first four games. Yes, the redshirt junior stepped in for an injured Salvon Ahmed last week and produced a career-high 118 total yards on 18 carries in a 45-19 win over BYU.

Yes, he runs with a surprising blend of forward momentum, shiftiness and compact brutality, like a bowling ball tumbling down a steep set of stairs.

He looks like a slot receiver, and he hits like a bag of bricks.

“I watch a lot of Alvin Kamara film, and I kind of feel like me and him are similar runners,” McGrew said. “I don’t know how to describe my game. I’m shifty in the open field and between the tackles, and then when I need to put my pads down, I’m a lot stronger now so I’m running through people.

“Yeah, I don’t know. I’m just a hard-nosed runner.”

Added Husky coach Chris Petersen: “I thought he did a nice job (against BYU). I thought he found the creases, put his pads down. He’s not the biggest guy, but I think he does a good job of falling forward. That’s what we want out of our backs.”

That’s certainly what UW has received out of both McGrew and 6-0, 210-pound redshirt freshman Richard Newton — both of whom could loom large if Ahmed sits again this Saturday when the Huskies host No. 21 USC.

McGrew’s frame is unremarkable.

But his game? It packs a punch.

“You’d watch him walk into the office (at St. John Bosco) and go, ‘Oh my gosh, that’s Sean McGrew?’” Negro recalled. “It’s just kind of remarkable to know the kind of player he is when you see him out of pads in a normal setting.”