ALLEN PARK, Mich. – A daily review of the hot topics coming out of Detroit Lions training camp:

• Referees were at practice Thursday and seemed to throw several flags throughout the session. Lions coach Jim Caldwell said the officials will be around for a few days to help the players become aware of new rules. The specific area of emphasis, Caldwell explained, is pulling of the jerseys. “It’s really going to affect everybody, you know,” Caldwell said. “It used to be if you grabbed a jersey and you restricted a player, if they saw the shoulders turn a little bit or maybe his stride changed, they would throw the flag. “But now, it’s any tug of the jersey, regardless of what it does to you and the quarterback can be looking over there and the foul can occur behind him and they still are going to throw the flag. So there’s a huge emphasis on that. Those are some of the things we have to make certain we get accustomed to.”

• Red zone was a focus of Thursday’s practice. On both fields, there was a significant period dedicated to work 20 yards from the end zone and in. Quarterback Matthew Stafford was fairly sharp during this period, highlighted by a leaping touchdown catch by receiver Kris Durham in coverage. It was a catch with a high degree of difficulty by Durham, who was rotating in on the same field along with the majority of the players who have been running with the first team.

• Speaking of the offense, this was the sharpest the offense has looked throughout the first four days. There were still some throwaways and dump-downs, but Stafford had a pretty good day, completing a large majority of his passes throughout the practice session. Eric Ebron, whose drops have been chronicled here the past three days, had a very nice catch at one point as the ball was headed out of bounds. That is the positive part of why the team drafted him in May.

• Rookie Kyle Van Noy appears to be starting to make an impact. The linebacker worked with the first-team defense during portions of Thursday’s practice and is starting to push to replace Ashlee Palmer at the SAM spot. After the draft, general manager Martin Mayhew indicated they believed Van Noy would be a starter pretty quickly. Tahir Whitehead also caught Caldwell’s attention, and while he isn’t a starter, the head coach said the third-year pro out of Temple continually shows up well on film. He won’t supplant Stephen Tulloch, but that, plus his special-teams ability, should put him in a good spot.

The Lions return to practice Friday at 3:30 p.m. for a practice open to the public.