Starting the Monday after Thanksgiving, youth sports, after-school athletic programs, and community centers in Boston must have concussion training and management procedures in place before teams can hit the court or field.

With its new city ordinance, Boston joins a growing effort to protect young athletes from the hazards of head injuries. A state law passed in 2010 already targets the problem in middle and high school sports, but some communities are trying to extend protections to younger children as well.