Raiders quarterback Derek Carr looked up at the scoreboard to check out the new guy, rookie safety Karl Joseph, and, as is often the case, didn’t really see him.

“He was a blur up there on the screen flying in there, trying to knock somebody out,” Carr said.

Observers have been trying to make out the blur, or listen for the loud thud, ever since Joseph was a 160-pound freshman middle linebacker at Orlando’s Edgewater High.

“I knew from the first minute of our first contact drill that Karl was a special player,” former Edgewater coach Bill Gierke said. “He generated tremendous power when he made contact … and he really enjoyed contact.

“So we put him at middle linebacker and he made so many tackles it was ridiculous.”

Joseph, who now stands 5-foot-10 and 207 pounds, never hit the huge growth spurt that would have allowed him to stay at the position.

“I thought I was going to be the next Ray Lewis,” Joseph said, laughing. “But my size … I started playing safety and cornerback my senior year to help make the transition to college.

“But you still see the linebacker mentality, and the aggressiveness, in the way I play.”

The transition was obviously a smooth one, as Joseph now stands as the Raiders’ starting strong safety when they host the Chargers today.

The transition was a bit rockier for opposing receivers. Joseph’s hits knocked seven players out of games during his career at West Virginia.

“I just see it and go,” Joseph said. “Not a lot of thinking on those, just second nature … I’m going 100 mph and then there’s a flash. I can feel it after and I get hyped.”

Raiders fans would get hyped for a big hit today, or even just some more steady progress. The rookie had 11 solo tackles and one pass broken up in his first two starts and narrowly missed both a sack and an interception against the Ravens.

“First-rounders are impact players, so he has to be well-rounded,” defensive coordinator Ken Norton Jr. said. “Great in coverage, great in man coverage, great in zone coverage, a great blitzer, tackler — we expect that guy to do all of those things.”

Joseph is getting more and more comfortable, after taking it slow in training camp and the first two games coming off knee surgery last year. That doesn’t mean he still isn’t mad at himself for the missed opportunities.

“I watch the plays I don’t make more than the ones I do, like that pick I dropped last week,” Joseph said. “I have watched that one 20 times. I misjudged it and reached out for the ball too early. I have to make those plays.”

But even the harsh critic will admit that the rookie is coming along nicely.

“Everything slowed down a little bit,” Joseph said. “I felt like I was able to have a better thought process pre-snap and I was able to communicate with the other defensive backs. I am just looking to improve every week, and it was a big difference from my first start to my second one.”

Joseph’s rapid improvement has been all the more striking since he discovered football late.

Born in Haiti, Joseph didn’t start playing football until he was 13 years old. He came to this country when he was 10 and begged his mom to let him play when he saw other kids doing it.

“I fell in love with the sport,” said Joseph, who played soccer in Haiti. “Learning the language and going to school was hard, and football definitely helped me fit in socially.”

His mom took a while longer to embrace football, going to her first game when he was a senior at Edgewater. “She still gets scared, and will turn off the TV when she is watching if I so much as fall down.”

Joseph went back to Haiti for the NFL draft, to watch and celebrate with his mom’s family.

Being picked in the first round by the Raiders was a special moment for Joseph, after people had been telling him his whole life that he was too small.

“That’s one of the reasons I play with a chip on my shoulder,” Joseph said. “I always heard I was too small, and I used that to my advantage.”

After a dominant career at Edgewater, Joseph didn’t get a lot of love from recruiters not because of his size but because they thought he was too slow to play safety.

“These so-called recruiting experts put a stigma on the kid,” Gierke said. “Karl Joseph is a football player. He has God-given ability. He is like a sponge. He is so coachable, and he is a leader. I had a good team already his freshman year here, and the seniors all looked up to him.”

Just like opponents, when the play is over.

Eight career forced fumbles at West Virginia, and five interceptions in four games before he got hurt his senior season, didn’t silence the doubters.

“Even coming out for the draft, people wondered if I can hit like that in the NFL or would I hold up,” Joseph said. “So I am still using that. That’s never going away until I prove that I am one of the best safeties in the league.”

In the preseason, Joseph learned he can’t hit NFL players up high like he could in college, and has lowered his pad level — “got better angles and went for their legs sometimes,” he said.

Raiders head coach Jack Del Rio has contained his enthusiasm, and he sat Joseph on defense the first two games to get him more mentally prepared and make sure his knee was sound.

“We like Karl, obviously,” Del Rio said. “We took him early in the draft. He’s working at it, doing a nice job with the different ways we’re trying to utilize him. Obviously, it’ll be big this week going up against a really good football team with a really good quarterback and really good tight end.”

Vic Tafur is a San Francisco Chronicle staff writer. Email: vtafur@sfchronicle.com Twitter: @VicTafur

Chargers (1-3) at Raiders (3-1)

When: 1:25 p.m. TV/Radio: Channel: 5 Channel: 13 Channel: 4695.7, 98.5, 102.9, 1350

Spotlight on: WR Amari Cooper. Everything points to a big day for Cooper. The Chargers are without starting cornerbacks Jason Verrett (on injured reserve with a torn ACL) and Brandon Flowers, as well as safety Jahleel Addae. San Diego is also going to have to pay extra attention to Michael Crabtree, who had 15 catches for 190 yards and three TDs the past two games.

Injury Report

Raiders — T Menelik Watson (calf) and RB Latavius Murray (toe) are out; TE Clive Walford (knee) and LB Malcolm Smith (quad) are questionable. Chargers — Flowers (concussion) and Addae (collarbone) are out; LB Denzel Perryman (shoulder) is questionable.

Big 3

San Diego has lost nine straight games to AFC West foes, its last win coming against the Raiders on Nov. 16, 2014.

First-round pick DE Joey Bosa, who held out and then missed time with a hamstring strain , will make his NFL debut for the Chargers.

Rookie running backs DeAndre Washington (6.4 yards per carry) and Jalen Richard (8.5) get their shot with Murray out. And don’t forget about fullback Jamize Olawale.

— Vic Tafur