NEW YORK -- The NFL is attacking the concussion issue on a team-by-team basis.

At the owners meetings in New York on Tuesday, Dr. Allen Sills, the NFL's chief medical officer, said the league identified seven teams in 2017 that had a higher incidence of preseason concussions than the others and "did a targeted intervention with those clubs." Sills said that process involved wide-ranging discussions with the football operations staffs of the teams that included the design of practice drills and which helmets players were wearing.

"In six of those seven clubs, the numbers did go down," Sills said. "Those seven clubs had 23 practice concussions as a whole in 2017, down to nine in 2018."

Overall, the league said, preseason concussions were down from 91 in 2017 to 79 this year, and there were zero on kickoff plays. The NFL modified its kickoff rules this year to make the play safer, as it traditionally has featured a significantly higher rate of concussions than other plays.

"We are cautiously optimistic about that result," Sills said of the preseason concussion numbers. "We are pleased to see that number go down, but we still have a lot of work to do. We are continuing a more in-depth analysis of the concussions that did happen during the preseason. Doing some of the same work we've been doing during the regular season, looking at video and seeing what the practice environment is -- seeing who was injured in what role. We are going to be doing more of a deep dive into that."

Sills and Jeff Miller, the NFL's vice president of player health and safety, said the league is also pleased about the results of its helmet rating system and is seeing more players change helmets to those the league rates as safest. The league handed out a flyer in the preseason ranking helmets on a green-to-red scale it developed in conjunction with the NFLPA, with green being good and red being bad.

Helmets that fall into the red category are being prohibited starting this year for new players and next year for players who were already in the league, giving them a "grandfather" year to find a helmet that works for them and still falls into the approved category.

Miller said the number of players wearing red-rated helmets was down from 230 last year to 40 as of Week 3 of this season.

Despite the greater emphasis on player safety, NFL football operations chief Troy Vincent said he doesn't want players worrying about getting flagged or fined.

On Sunday night, Kansas City Chiefs rookie linebacker Breeland Speaks said he didn't take Tom Brady down because he was concerned about a roughing-the-passer penalty in the fourth quarter of Kansas City's 43-40 loss at New England. Brady eluded Speaks and ran 4 yards for a touchdown to give the Patriots the lead.

"You gotta play," Vincent said Tuesday at the fall meetings. "You hope that no player is thinking about a rule. We want them to play [with a] free mind where you're just free and you play.''

The NFL has emphasized this season that officials should penalize defenders for landing on quarterbacks with all or most of their body weight.

NFL officials threw 53 penalty flags for roughing the passer over the first six weeks of the season, compared with 38 in 2017 and 32 in 2016 over the same stretch of games.

Overall, roughing-the-passer calls are down since the competition committee clarified to game officials the techniques used in such hits during a conference call last month. There were 34 roughing calls through the first three weeks and 19 in the three weeks since the conference call.

Vincent said the league didn't advise officials to cut down on the calls, but emphasized that they make sure they see the play clearly.

"If you don't see the complete play, don't call it,'' Vincent said. "That was a directive from the competition committee. That was always the point of emphasis but after the [conference] call and after watching the video, the committee and our coaches [said]: 'If you don't see the complete play, we ask that you leave the penalty in your pocket.'"

The Associated Press contributed to this report.