NAPA — Trent Richardson is motivated to jump start his career again.

The Raiders running back took the first step in that direction when he made his training camp debut Thursday and set the record straight on his absence from the first five days of practice.

“I had pneumonia,” Richardson said. “It was in the back of my lungs, so that’s nothing to play with.”

Richardson heard reports that suggested he was overweight, and while he wouldn’t say he grew frustrated by them, he responded.

“I was nowhere near overweight,” he said. “I actually came back in around 222. I was actually below what coach wanted me to come in at.”

Richardson’s comments came four days after coach Jack Del Rio praised his conditioning as well. Richardson first began working out on the side on Monday and was able to practice after passing a conditioning test Wednesday.

“In the conditioning test, I killed it,” Richardson said. “I actually wanted to practice after the conditioning test but coach wouldn’t let me. “

Richardson said he had a cough starting two weeks before he came to camp and eventually had a headache for two days. That sent him to the doctor and he received the diagnosis and then learned there’s a bit of family history with the infection.

“I came to find out a few of my close relatives died from pneumonia,” Richardson said. “I didn’t even know it.”

By policy, Del Rio does not discuss injuries until the season starts and the league requires updates and so he remained vague while Richardson was out.

That naturally led to speculation about a player who flamed out in Indianapolis. He was inactive for the Colts’ final two playoff games last season and there reportedly were concerns about his weight.

Richardson was cut by the Colts in March and signed with Oakland — a franchise well known for its attempts at reclamation projects.

“I’m very driven,” Richardson said. “First of all because I’ve got kids. Second of all, I’ve got a lot to prove to myself. Everybody wants to put pressure on me, but that pressure is nothing but greatness. These people want me to be great out here.”

Greatness was expected out of Richardson when he was drafted No. 3 overall in 2012 by the Cleveland Browns. He had a solid rookie year with 950 yards and 11 touchdowns, plus 51 receptions.

Two games into his second season in Cleveland, the Browns traded him to the Colts. Despite scoring a touchdown on his first career carry with Indianapolis — in a 27-7 Colts win over the 49ers — Richardson never got going. He averaged just 2.9 yards per carry that season and rushed for 519 yards last year (3.3 per carry).

Richardson was suspended for last season’s AFC title game after reportedly missing the team’s walk-through the day before because of a family emergency that he didn’t notify the team about.

Looking for a fresh start in Oakland, Richardson grew eager over the past week because he couldn’t get on the field.

“We’re a team that has a new offensive coordinator — everybody’s new, so we’re growing together. I felt like I was missing time on that,” Richardson said. “I was going hard in the classroom. I was going hard when I was sitting out here just looking on the iPad. Coach always says, ‘Stay mentally strong with everything.’ That was just me being mentally strong.”

There wasn’t any easing in for Richardson. Fellow running backs Roy Helu Jr. and Michael Dyer missed Thursday’s practice with undisclosed injuries, so Richardson was thrust into second-team repetitions.

“He looked pretty good,” offensive coordinator Bill Musgrave said. “He hit a couple holes with good timing so we were glad to have him.”

* After a tough start to camp for the secondary, there were several nice plays made Thursday.

During a late 11-on-11 portion, D.J. Hayden had a nice pass breakup on a ball thrown to Kenbrell Thompkins, who was shaken up on the play. Just a couple plays later, Hayden intercepted a pass by Derek Carr.

The final play of practice was a Tevin McDonald interception of a Christian Ponder pass. Malcolm Smith should’ve had a pick during a 7-on-7 session but dropped the ball after making a perfect break toward it.

Keith McGill also had a couple nice plays on the day. Early in practice, he broke up a Carr pass to tight end Mychal Rivera on a double move throw. Later, he used every inch of his 6-foot-3 frame to tip away another pass to Rivera on the sideline.

While that showed progression for the defense, Musgrave wasn’t happy.

“Today was a day that we definitely want to learn from,” Musgrave said. “As soon as we learn from it, we want to forget it because it wasn’t the way you play winning football.”

* Menelik Watson missed practice with an undisclosed injury, leaving Austin Howard to take the first-team reps at right tackle. Watson did work out on the side field.

Tight end Clive Walford still hasn’t joined the team and Musgrave acknowledged he’s falling behind.

“You can’t make up those days you miss,” Musgrave said. “I know he’s working hard to get healthy and get back out here. So, we’re looking forward to that day.”

Wide receiver Rod Streater remains on the non-football illness list and defensive tackle Stacy McGee on the physically unable to perform. Fullback Jamize Olawale didn’t practice and was seen with his right foot in a boot and walking with the use of crutches.

* As for a few other practice highlights, Kris Durham made a tremendous catch on a pass from Matt McGloin. He one-handed the ball in the front corner of the end zone and was ruled in bounds for a touchdown.

During that same 11-on-11 session, Carr rolled out and rocketed a pass that Michael Crabtree made a nice grab of in the end zone, but he was ruled to have caught it out of bounds.

In 7-on-7 work, Andre Holmes had a bad drop on a wide open pass. Right after that, Brice Butler zipped in to make a catch and ran around several defenders in a nice run after catch display. That is until Jonathan Dowling stripped him of the ball.

Cody Fajardo had a nice throw in 7-on-7 work when he hit Durham on about a 20 or so yard in route.