He made the most of those reps, intercepting Colin Kaepernick twice during full-team drills, including the first play from scrimmage and ending a two-minute drill for the starting offense.
On the first play of 11-on-11s, Kaepernick looked for wideout Anquan Boldin deep down the middle of the field. The pass, which was underthrown, was undercut by Cox for the interception.
His other interception came on the second play of the two minute drill when it was starters vs. starters. Kaepernick took a three-step drop and looked for Quinton Patton on a back-shoulder throw on the right side of the field. Cox read it quickly, broke on the ball and came away with the interception ending the drill.
Wednesday's performance bodes well for Cox as he showed versatility in being able to play on the outside as well as inside, where he's been working as the primary nickel corner with the starters.
Second-year player Darryl Morris had another strong day with three pass breakups, including two on back-to-back plays during seven-on-seven drills thrown by Kaepernick. They came on throws to Brandon Lloyd and Stevie Johnson - while the third occurred during the full-team session while covering Boldin in the left flat.
Norris is off to a strong start and looks like a favorite to land a roster spot among the team's cornerbacks - not only because of the progress he's shown defensively, but also because of what he brings to special teams coverage.
Defensive backs early in practice were making a habit of going for the ball right as it hit receivers hands. Both Cox and Morris stood out during the seven-on-seven period, but rookie Dontae Johnson also swatted a pass out of the hands of Boldin on a slant route over the middle.
It's tough to judge how well rookie running back Carlos Hyde is playing given the limited contact allowed in training camp. But if Jim Harbaugh's audible praise is any indication, Hyde is doing just fine.
After a number of touches, including runs and check down receptions, Harbaugh would loudly praise his new running back, who received the bulks of the reps alongside Jewel Hampton.
Before practice during his session with the media, Harbaugh channeled his offensive coordinator, who likened Hyde's performance to that of Frank Gore. The team is using Gore very sparingly with Kendall Hunter (ACL) and LaMichael James (dislocated elbow) on the shelf.
"And these aren’t my words, these are Greg Roman’s, now, but I thought it was pretty astute that he said that," Harbaugh noted. "Carlos gets football, understands football, it’s natural for him to understand the game, similar to Frank Gore. And we're seeing those things, and both are very good signs and bode well for us.”
Quinton Dial and Tank Carradine received a number of reps Wednesday as Justin Smith, Ray McDonald and Demarcus Dobbs all missed practice. Smith (shoulder) and McDonald (leg) heave dealt with injuries that have caused them to miss all of camp to this point, while Dobbs sat out practice for the first time Wednesday.
Dial and Carradine looked very strong in individual drills against offensive linemen and look like they will add some welcomed depth to a group that was five-deep for most of the 2013 regular season.
Dial's versatility is one of his best assets. His ability to play nose tackle and the end spots could make him a valuable piece off the bench, particularly against the run.
Carradine's heavy hands and quickness as a pass rusher stood out. And after playing as a traditional 4-3 defensive end at Florida State, he looks like a nice fit in passing situations to spell McDonald and/or Smith. But he will still have to earn those snaps by overtaking Tony Jerod-Eddie and Dobbs, who have done most of their work with the first team to this point.
"I thought there were some really good things, along with Quinton Dial," Harbaugh said over the weekend. "I’m very, very pleased to see both those guys in pads, in real full-speed competition with the pads. I thought that Tank especially is even further along, some real heavy hands and strong. He’s off to a strong start.”
Skuta was used primarily with the first team in base situations while Lemonier came in with the nickel package.
Lemonier hasn't had a standout training camp to this point, but he hasn't been playing poorly either. He's been asked to do more in coverage, which clearly isn't his strength after playing defensive end at Auburn. We'll have a better idea of Lemonier's progression from his rookie year during when the preseason games start.
Jimmie Ward's already received high praise for his work to this point and he's taken advantage of playing with the first team with Culliver and Brock out of the action.
He still has his rookie moments during individual drills, but is a better performer in 11-on-11s.
If there's one concern about Ward, it's his weight. He's listed at 193 pounds, but that might be a little generous. Considering how often the nickel corner is around the line of scrimmage, Ward could stand to bulk up 10 or 15 pounds, which would also help out when covering tight ends and playing safety.
Michael Crabtree left practice about halfway through accompanied by a member of the training staff. He was limited in his participation during team drills.
If Crabtree was injured, it didn't appear very serious. There wasn't a noticeable limp when he left the field.
But given his injury history, it's something to keep an eye on. Crabtree dealt with a right foot injury during training camp in 2011 after suffering a stress fracture in his left foot in 2009. Last season he sustained a tear in his right Achilles during minicamp.
E-mail Niners Digest: NinersDigest@gmail.com
Follow Editor in Chief Chris Biderman on Twitter.