Today’s card of the day is the “Football Equipment” card from the 1952 Parkhurst Canadian football card set. To my knowledge, it is the only football card featuring a jockstrap.
There are 100 cards in the 1952 Parkhurst set: 81 player cards and 19 “How to Play Football” cards like the Football Equipment card. The 81 player cards picture players from the four Interprovincial Rugby Football Union (IRFU) teams: the Toronto Argonauts, Montreal Alouettes, Ottawa Rough Riders, and Hamilton Tiger-Cats. In 1958, these four teams would form the East Division of the Canadian Football League. The five teams from the Western Interprovincial Football Union (WIFU)–the Edmonton Eskimos, Winnipeg Blue Bombers, Calgary Stampeders, BC Lions, and Saskatchewan Roughriders–would form the West Division.
In 1952, the top teams from Canada’s three football leagues–the IRFU, the WIFU, and the now-defunct Ontario Rugby Football Union (ORFU)–participated in a playoff for the Grey Cup Championship. Remarkably, it took twelve games to determine a champion–the Toronto Argonauts–from seven playoff teams. Wikipedia has a picture of the playoff bracket.
You can see the full 1952 Parkhurst football card set in the Gallery.