Mr. Bettman wrote his response in lawyerly language and footnoted it throughout, most likely knowing that it would be used in litigation and made publicly available. (“The N.H.L. believes that such tactics are highly inappropriate, and the court overseeing the litigation has admonished the parties not to litigate the case in the media,” he wrote.) It never addresses the specific questions, laying out the N.H.L.’s case in broad sweeps rather than in a question-and-answer format.

“We respond to each of these subjects below and in the course of our discussion hope to answer the questions you posed,” the letter reads.

The letter addresses related issues, such as fighting (relatively few concussions come from fighting, Mr. Bettman said) and the league’s history of concussion oversight and protocols, which have been widely criticized as little more than window dressing.

Mr. Bettman repeatedly blamed the media for spreading the fear of C.T.E., and accused the plaintiffs in the concussion case for a public relations assault on the topic. He ended the letter by retelling the story of the former N.H.L. player Todd Ewen, who died of a reportedly self-inflicted gunshot wound last year at age 49. He was the latest in a string of former enforcers, including Boogaard, Bob Probert and Wade Belak, who died young after displaying symptoms related to C.T.E., including memory loss and depression.

Unlike some of the other brains posthumously examined, however, Ewen’s did not show signs of C.T.E. That surprised Ewen’s wife, who said she hoped that others would take comfort that C.T.E. might not always be the culprit of a loved one’s unraveling. Mr. Bettman saw that as proof that public opinion had gotten unreasonably ahead of science.