NEW YORK—The number of concussions suffered by NFL players dropped this season, according to injury data released Thursday by the league.

According to the NFL, there were 228 concussions suffered by players this season, down 13 percent from the 261 concussions suffered during the 2012 season.

Players suffered 252 concussions during the 2011 season, according to the league’s data.

The NFL has modified its procedures in recent years for identifying and treating concussions, requiring a player with concussion symptoms to be removed from a game or practice and cleared by an independent neurologist before returning to play. The league also has attempted to reduce concussions by penalizing and fining players for hits to the head of an opponent deemed to be in a defenseless position, such as a quarterback delivering a pass or a receiver making a catch.

The players’ union has access to the same injury data.

DeMaurice Smith, the executive director of the NFL Players Association, said Thursday: “It’s a reduction in numbers. I’m not a statistician. But any person who has worked on budgets or worked on anything that we look to be quantified knows that numbers one year or one moment can go up. They can go down. The real questions are: Are the differences statistically significant? The real question, I think, is what do you take away from those changes in numbers? And yes, there has been a decrease. Frankly, I would like to see what those numbers look like over a three- [or] four-year period to make a decision as opposed to a one-year period.”

Smith said there also was a change this season to the injury management system for collecting the data.

“I think it’s important for us to know whether a difference in that system might have caused a difference in the reporting…. We’ll crawl through the numbers during the offseason and take a look,” Smith said. “But this was the same way that we didn’t instantly react to an increase in injuries at the earlier part of the season…. As the weeks went on, the numbers normalized. And that’s because that’s what you do. You engage in a process to measure numbers over a period of time in order to define or discern what the right conclusions are.”

Earlier this month, a federal judge declined to grant preliminary approval of a $765 million settlement between the league and former players who sued over concussions, asking for more financial analysis of the proposed settlement.

The league’s injury data released Thursday indicated that anterior cruciate ligament injuries to players’ knees also were down this season. There were 57 ACL injuries this season, compared to 63 such injuries last season, according to the data. Injuries to the medial collateral ligaments in players’ knees remained roughly the same, according to the data, with 133 such injuries this season after 132 last season.