Two days after the Vikings lost to the San Diego Chargers, a game in which Christian Ponder was sacked four times and threw an interception, the second-year quarterback was still taking the blame for the offense’s poor performance.

Vikings QBs were sacked five times in the game, and although RT Phil Loadholt and LT Matt Kalil were each beat on two of them, Ponder said the reason for the sacks was that he was not stepping up in the pocket.

“I’ve got to do a lot better job, and after watching it (on film), stepping up in the pocket is the biggest thing for me,” said Ponder. “It’s something we kind of focused on (Sunday), doing some drills. Hitting that last step in the drop, setting the depth and just moving forward.

“A couple times I tried to escape outward rather than moving forward and that hurt me. But it’s easily correctible. It was something I was in the habit of doing all camp until Friday, but we’ll change it.”

Frustrating fumbles: Coach Leslie Frazier is clearly frustrated with the turnovers against the Chargers. After the game, Frazier mentioned that the running backs vying for a third backup position (Matt Asiata, Lex Hilliard and Derrick Coleman) fumbled in the game -- and Coleman was waived onSaturday. On Sunday, Frazier still wasn’t pleased with the performances Friday.

“Nobody distinguished themselves the other night. It’s still an open competition,” said Frazier. “You have to keep your eyes on the guys that are on our roster, but you are also looking to see what happens around the league.

“We’ll see what happens on Thursday night (against the Texans). Hopefully, someone will take the bull by the horns and really separate themselves and say, ‘that’s my job on this football team.’ But, we’ll see.”

Carlson returns: TE John Carlson returned to practice for the first time since July 31 when he sprained his MCL. With two weeks of practice left before the first regular season game, he has a lot of catching up to do.

Frazier said Carlson moved around pretty well at practice and they would try to throw a lot at him before the first game, but that he won’t play Thursday against the Texans. Regardless, Carlson’s QB is glad to have him back.

“I know he was excited to get out there at practice today,” Ponder said. “He’s a guy we could use and are happy to have him back.”

 Injury update: Vikings players are bouncing around the roster like pinballs. In Friday’s game, the Vikings had four of the team’s six safeties not playing due to injury. Mistral Raymond (lower back) and Robert Blanton (hamstring) didn't dress, and Andrew Sendejo (ankle) and Eric Frampton(groin) left the game with injuries.

Blanton and Frampton returned to practice Sunday, but Raymond and Sendejo didn't participate. Coach Frazier was asked if he would be searching the waiver wire for secondary help.

“Rick (Spielman) and the scouts are always going to be looking at the wire to see who could potentially be there to help us, so that will be ongoing for sure,” said Frazier.

CB Josh Robinson (concussion), Ryan D’Imperio (shoulder) CB Chris Carr (lower back), CB Marcus Sherels (ankle) and RG Geoff Schwartz (sports hernia) also didn't practice. Although Frazier said the Schwartz was moving well and may be able to get back to practice soon.

CB Chris Cook, who suffered a concussion in the Bills game, returned to the field and DT Letroy Guion, who missed the Chargers game after aggravating the PCL in his right knee, returned to practice with his helmet. Neither player will play Thursday against the Texans. 

LB Larry Dean (shoulder) returned to practice and should see some action against the Texans on Thursday, when the reserves will get the bulk of the playing time.

For more Vikings news and notes, follow Joe Oberle on Twitter @CBSSportsNFLMIN.