Boxing, football, bodybuilding and jihad: most of those who have carried out terrorist attacks in France also played organised sport, and clubs, particularly in the Paris region, are worried.
The problem might still be rare, but clubs are training their staff to detect radicalisation on the playing fields in a country that has been frequently targeted by extremists.
"Leo, a young footballer, has changed recently. He is late to training because he says he has to go to the mosque to pray beforehand, and he refuses to shake hands with women. What do we do?"
Faced with this question from an instructor, the eight club officers from different sports round the table think hard.
At the start of this training day, the only one of its kind in France, at the headquarters of the Ile de France sports committee in Gentilly, a suburb south of Paris, the regional vice-president, Patrick Karam, had exhorted those present to be "intransigent" in the face of radicalisation.
According to French government figures, of the 8.7 million registered members of sports clubs in France, about 829 individuals had been flagged as radicalised by November, 147 of those in the Ile de France.
The proportion might be small, but sports club, led by martial arts, football and bodybuilding are — the government says — the number one place of radicalisation in France, ahead of places of worship.
In Lagny-sur-Marne, in the eastern suburbs of Paris, the local government banned two coaches suspected of radicalisation at a football club in November.
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In Paris, a former junior judo star was thrown off a coaching course because "he refused to salute the mat, saying that he could only bow his head before the Prophet and that he did not wish to speak to women", one of the officials who tried in vain to persuade the trainee to change told AFP.
The home-grown terrorists who have carried out attacks in France have frequented sports clubs, and several were linked to each other in this way, said one of the speakers at Gentilly, Mederic Chapitaux.
"We are not asking you to be informers but to play your role as educators and to protect these youngsters," said Mr Karam, assuring the participants of "absolute confidentiality" in the reporting process to protect them from possible retaliation in their neighbourhoods.
These are risks that one of the participants at Gentilly, Corinne — not her real name — knows well. Her son "was beaten up one night by a gang" who did not want the sports association she runs on their turf in the eastern suburbs of Paris.
Corinne is angry with the local mayor who ended up closing the sports hall.
"The unemployed young people have been trapped by drug trafficking or the Muslim fundamentalists. Several went to Iraq or Syria, two are in prison for planning a terrorist attack."
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As for the case of Leo, a dialogue with his brother and the support of social services allowed the young footballer to resolve his family problems that had pushed him to breaking point.
"We kept the channel with him open, which is essential," said the instructor who had come from National Committee of Liaison and Prevention (CNLAPS), which serves as a resource for clubs and associations.
The CNLAPS instructor offered another case study based on real characters.
"Dany and Robin, 24-year-old twins who had served time in prison for drug trafficking and had become very religious, divide their time between the mosque and sport. They have married and envisage going with their wives to Egypt to learn Arabic. They hang out with two youngsters from your boxing club."
In the face of a "strong signal" of the departure of a family member who might be going to Iraq or Syria and the risk of "infection" of the two young men, the majority of participants choose to signal the case to the authorities.
"You must not hesitate. The recruiters move very fast," the instructor said.
After the session, a number of those present expressed their satisfaction.
Corinne said she "feels less isolated" and that she sees that there are mechanisms "to help us".
"This gives us guidelines and tools just in case," said Christine, who helps run a football club in the outskirts of Paris.