The second and third concussions were in 2015 and 2016 during football games. Orsini said that afterward, his son was sensitive to light and noise, experienced headaches and was lethargic. His son, he recalled, sat slumped at the table during meals. Again, within a few weeks, doctors cleared him to return to play. Orsini said that when he asked the doctor whether his son should stop playing football, he was told there was no medical evidence that he should cease playing.

“The moment for me started when he repeatedly got diagnosed with concussions and the doctors kept telling me there was no reason for him to not keep going,” Mr. Orsini said. Having worked as a plaintiff’s attorney, he was alarmed. “His mother didn’t question the doctors, but in my profession it is an impossibility.”

Mr. Orsini said he was surprised that his son’s doctors appeared to be sanguine about the dangers of the sport. So he began doing his own research and found, among other things, studies by researchers at Boston University that said that boys who began playing tackle football before the age of 12 had more behavioral and cognitive problems later in life than those who began playing the sport in their teenage years.

Mr. Orsini said he tried unsuccessfully to discuss these findings with his ex-wife.

Mrs. Orsini declined to be interviewed. But her lawyer, John N. Demas, said she considered her son, now a junior in high school, mature enough to understand the risks of the game and to make up his own mind. She also felt reassured that her son’s coaches were well-trained at spotting and caring for concussed players, and that doctors had declared him free of symptoms from the concussions.

“The truth is, this young man loves to play football and understands the dangers, and based on the science now, his mom thinks the benefits are worth the risks,” Mr. Demas said on behalf of Mrs. Orsini.

Mr. Demas added: “Where we are with the science of it, I don’t know if there is enough evidence to say it’s inherently dangerous.”

Mr. Demas said that the Orsinis have joint legal custody of their son, and that Mr. Orsini’s attempts to block their son from playing football amounted to one parent acting unilaterally. In seeking to alter their custody agreement, Mr. Demas said, Mrs. Orsini was only trying maintain the status quo.