Travelers Cos. Inc. is suing the National Football League and more than two dozen other insurers in New York state court, saying it has no obligation to defend the NFL in a prescription drug-related lawsuit filed by more than 500 former players. In a complaint filed July 3 in New York State Supreme Court, Travelers said it issued excess liability insurance policies to the NFL between 1991 and 2002. The NFL has demanded that Travelers defend and indemnify the league in a class action lawsuit that was filed in May in San Francisco federal court, the complaint says.