Throughout his life, Vikings safety Harrison Smith has had his share of nicknames.

"H" -- that's the easy one.

Or Harry, as teammate Chad Greenway now calls him.

Once Smith had long hair, which led to his temporary identity as "Tarzan." On his arrival at Notre Dame in 2008, Smith was referred to as "Hayseed," because, in his words, "I was from the sticks in Tennessee."

But Vikings defensive coordinator Alan Williams may have found the most appropriate nickname: "The Eraser."

Williams borrowed that from mentor Tony Dungy. But it's exactly what he wants his safeties to be and what he's getting right now from Smith, a 23-year-old rookie who's more instinctive and fearless than most.

"He can erase some mistakes other people make," Williams said. "And that's been the biggest thing he's done."

Which brings us to safety Jamarca Sanford, who gushed about Smith as if he'd found a new best friend. In many ways, he has.

"Harrison's a smart guy," Sanford said. "Catches on real fast. He's the kind of guy who can see something in the classroom and take it to the field. ... It's like being back there with a veteran."

You might not have noticed Sunday, but Sanford was beaten twice for game-changing TDs by Lions receiver Calvin Johnson.

The first came late in the first half when Johnson ran a post route and used his 7-inch, 40-pound advantage to shield Sanford from the ball. A perfect Matthew Stafford pass hit Johnson right in the hands in the end zone.

The second Johnson touchdown came after halftime when he twisted Sanford like a circus balloon, gained 4 yards of separation and strolled under a 65-yard TD toss.

What's that, you say? The box score of the Vikings' 20-13 victory doesn't show Johnson scoring? Oh, that's because of "The Eraser."

On that first near-TD, Smith darted to the middle of the end zone and put a shoulder into Johnson's midsection right after the pass arrived. Johnson couldn't hold on. On the third-quarter bomb, Smith recovered from the back side to erase Sanford's miscue, producing a key if underrated pass break-up.

Noted Williams: "That wasn't necessarily his play."

The Lions could have tied the score on that bomb. Instead, 21 seconds after Smith's eraser moment, Marcus Sherels returned a punt 77 yards for a touchdown and the Vikings led 20-6.

These are exactly the plays that made the Vikings fall in love with Smith. The attraction heightened during their January week together in Mobile, Ala., where the Vikings staff coached Smith's North squad at the Senior Bowl.

The Vikings already were sold on the safety's intelligence. But in working with him, they recognized his prodigious alertness. And they confirmed that even with Smith's large frame (6-2, 215 pounds) he wouldn't be out of his element in pass coverage.

"Most big players get to be a little leggy; they don't change directions well," Williams said.

"But Harrison could do that. And he was a smart, instinctive ballplayer."

No wonder General Manager Rick Spielman did everything to assure Smith would be a Viking. Spielman engineered a trade with Baltimore on the draft's first night, moving the Vikings up from No. 35 to No. 29.

There he nabbed Smith and didn't have to deal with a sleepless night of waiting and hoping.

Now Smith's rapid maturation has aided a 3-1 start. And his "Eraser" skills certainly changed the narrative for Sanford last week. Instead of being skewered for allowing two Johnson TDs, Sanford received endless praise for his hustle and unselfishness.

Naturally, Smith's crushing hit on Johnson stands as his trademark moment.

"He's actually a lot bigger than I realized," Smith said. "Still, for me, once a play starts, you just react and play ball."

Added Sanford: "He gets to talking smack every now and then. I saw him talking one time [to Johnson]. He's like, 'You're getting scared. Coming across the middle. He's scared! He's scared!' "

Erasing mistakes is one thing. Erasing Calvin Johnson is on a whole different level.

Dan Wiederer • dan.wiederer@startribune.com