On March 31st, 1951 the Toronto Maple Leafs and Boston Bruins battled in what was described as "one of the most gruelling NHL playoff games on record." The game went into overtime, but was never completed.
Why was it never finished? Because of Sunday.
Back in those days the city of Toronto had a municipal bylaw that forbade events such as professional sports on a Sunday.
Well game 2 of the Leafs-Bruins opening round series started on Saturday, but threatened to pass over midnight into Sunday, heaven forbid. So when the first overtime period ended minutes before the clock struck twelve, the game was called. Final score 1-1.
Officially the game never counted, although the player's statistics did. Here's Jim Vipond's account from the April 2nd, 1951 Globe and Mail:
"Although the statistics will be incorporated into the record book to recall a bruising night in big-time hockey, the result is wiped out. If necessary to declare a winner, the game will be replayed as the 8th contest at the conclusion of the 7 game series."
That meant after seven periods and 140 minutes of the most physical hockey ever played, the Bruins held just a 1-0 series lead, with games three and four moving back to Boston. The Leafs would come back to win the series 4 games to 2.