Enrico Locci - Getty Images
The short story shorter:
Fans were banned from the stadium due to "security concerns."
Massimo Cellino invited fans, sold tickets anyway and got all dramatic.
“Cagliari Calcio and its engineers consider the structure to be adequate and secure.
“This move is absolutely peaceful and was pushed by the pain and frustration of defending our right to exist.”
The Man called him an idiot and cancelled/postponed the game.
Rumblings of Roma potential requesting a technical forfeit, but if every club requested a 0-3 reverse each time an Italian owner did something stupid...
Non-update Update: Roma wants that forfeit, obviously, because this match cancellation was entirely Cellino's fault. Based on the laws of good sense*, they should get it, too.
* - I realize these do not apply in Italian football.