From nine rows up, Beltran Diaz looks out on one of soccer’s most coveted turfs and considers what has changed since his grandfather first bought Real Madrid season tickets a half-century ago. It was only recently that cigarette smoke still gathered in cumulus billows around the lights, while those below guzzled cups of Mahou beer. And it also hasn’t been long since soccer here, like everywhere in Europe, was plagued by the furies of the hooligans, the politically-inflected violence of the men known locally as ultras, who occupied prominent seats and often whipped the game into a frenzy. Here in...