An 11-year-old boy has been stabbed to death by a masked assailant while playing on a football field in a small Spanish town south of Madrid, state broadcaster RTVE reported on Sunday. The assailant had appeared suddenly on the field in Mocejón before stabbing the boy with a sharp implement. By the time paramedics arrived, the 11-year-old had suffered heart failure and could not be revived, the report said. A large operation has been launched to find the unidentified assailant. Castilla-La Mancha President Emiliano García-Page said he was shocked by the crime and expressed his condolences to t…