We find meaning in sport, and escapist joy, because we have become sufficiently refined and civilised to enjoy a gladiatorial spectacle in a safe context. But when the real thing is near at hand, when genuine violence enters the stage, sport suddenly seems like a luxury we can no longer afford. That is why this week's terrible events in Lahore have shocked sportsmen and fans more than anything since the Munich atrocities of 1972, writes Ed Smith in the Telegraph.