To the Vikings, he is “Hit Man” or “Dirty Harry.” A dozen years ago in Tennessee, Harrison Smith was known by another nickname.

When Smith was in eighth grade in Knoxville, his youth coach was Tim Irwin, a former Vikings tackle who is a juvenile court judge in the city. Back then, Smith was starting to carve out his reputation for belting out hard hits.

“They called him ‘Bonecrusher,’ ” Irwin said. “He was like a heat-seeking missile. He was such a strong, fast kid, and he was just way above everybody else in hitting ability.”

The hits have kept coming over the years, for Knoxville Catholic High School, for Notre Dame and now for the Vikings.

The fourth-year safety has had several plays this season that would be worthy of “Crunch Course,” if NFL Films still put out such videos.

In the opener, Smith leveled San Francisco quarterback Colin Kaepernick before he could get out of bounds on a run. In October, he drilled Denver wide receiver Demaryius Thomas following a short reception, knocking him out of the game briefly.

November has seen Smith wallop Chicago running back Matt Forte after he caught a screen pass and clobber Oakland wide receiver Amari Cooper following a catch. Forte missed three games with a knee injury sustained in the hit before he returned Thursday night at Green Bay.

“He definitely puts fear in an opponent’s eyes when they see him back there,” said Minnesota cornerback Captain Munnerlyn. “When they’re running an inside route, they know that Harrison Smith will knock you out. It definitely helps us out knowing we got a hard-hitting safety who doesn’t mind throwing his body in there and making plays.”

Munnerlyn calls Smith “Dirty Harry” after Harry Callahan, the San Francisco detective played in the movies by Clint Eastwood. Like Callahan, Smith is an enforcer.

A more popular nickname for Smith is “Hit Man” or “Harry the Hit Man.” Vikings broadcaster Paul Allen coined those before last season.

“It was after a practice in Mankato in the preseason,” Allen said. “I told him I’m thinking of calling you ‘Harry the Hitman,’ but I don’t want to go with it if you don’t like it. So he liked it, and a few other teammates seemed to like it.”

So do fans. Tony Jimenez, a Vikings booster from Bakersfield, Calif., who admired Smith’s aggressive style so much he adopted him as his favorite player during his rookie year of 2012, showed up for training camp last summer wearing Smith’s No. 22 jersey with “Hit Man” on the back.

Knoxville is where Smith first became a feared defender.

While Irwin doesn’t like to talk about it much, Smith once broke a player’s leg in practice with a vicious tackle. It happened on a day Irwin wasn’t there and the workout was run by an assistant.

“He busted through the secondary and before anybody could get him stopped, he’d run over a smaller kid,” Irwin said. “He had a badly broken femur, and he didn’t play football again. But it wasn’t anything that Harrison did wrong.”

There at least was a silver lining to the incident. Although the injured kid never played football again, he turned to tennis and had a lot of success.

“You never want to hurt anybody,” Smith said in looking back at the incident. “I try to keep it clean.”

Smith also felt bad about Forte being hurt Nov. 1 at Soldier Field. Smith led with his shoulder, and there was nothing malicious about the hit.

“It’s been all legal, what he does,” Munnerlyn said. “He’s been definitely doing a good job of lowering his target and running through people.”

With the NFL going to great lengths in an attempt to eliminate injuries, rules have been changed in recent years. Leading with the head or going after the head or neck area now draws a flag.

The hit Smith had on Cooper following a 15-yard reception Nov. 15 initially was flagged. But officials consulted and determined Smith led with his shoulder, so the penalty was waved off.

“I’m not playing for the big hit; that’s really not my game,” Smith said. “My game is making tackles and getting in the right spots and making the plays. … If (people) want to recognize me for (hard hits), that’s fine, but I’m just all about making the tackle.”

Still, Smith agrees a hard hit can fire up his team. He also admits to having watched his share of big-hit videos while growing up.

Before concussion prevention became such an important issue, the NFL put out highlight videos with such titles as “Crunchtime” and “Crunch Course.” Smith paid special attention to what defensive backs dished out.

“When I was in high school, we used to watch Steve Atwater hits and that kind of stuff just to get excited,” Smith said. “We’d watch Brian Dawkins or Sean Taylor. (Taylor) had a hit in the Pro Bowl (after the 2006 season) against the punter (Brian Moorman). He smoked the punter on a fake punt.”

After he entered the NFL, it didn’t take long for Smith to gain his own reputation for smoking guys. In his fourth regular-season game, he walloped Calvin Johnson in the end zone, forcing the Detroit star receiver to drop a possible touchdown pass in an eventual 20-13 Minnesota win.

“It caused Calvin to go woozy, and it absolutely changed the outcome of the game,” Allen said.

The greatest hits of Smith have continued. When Smith leveled Kaeparnick with his shoulder on “Monday Night Football,” it got plenty of attention.

The hit on Thomas forced the receiver to go to the locker room for evaluation before he was able to return. After the game, Thomas said, “I haven’t got hit that hard in a minute.”

The Vikings lost the games against the 49ers and Broncos. However, the Forte tackle proved important because the Bears star was lost for the game early in the third quarter of what would be a 23-20 Minnesota win. The hit on Cooper early in the second quarter helped set the tone on defense in a 30-14 Vikings victory.

“He’s an aggressive dude,” said Andrew Sendejo, Minnesota’s other starting safety. “He’s not scared of contact. He usually has one a game where he hits a guy pretty good. There’s a lot of them on film.”

There are plenty of highlights online of hard hits by Smith. They’re just not put together in a neat package by NFL Films.

Follow Chris Tomasson at twitter.com/christomasson