D-cards represent cards from various types of bread/baking companies. These were usually packed in loaves of bread or other baking-related items.
Most issues were relatively standard, but some unique D-cards do exist. The D146 Donut Corporation of America cards, for example, were cutouts off of donut boxes.
Most bread issues are relatively scarce by comparison to other more common candy and tobacco cards. These were almost certainly printed in much smaller quantities and practically every bread issue is a somewhat difficult one to find.
It is worth noting that at least one other set could possibly be classified as bread football issue. The D96 set features college pennants for various schools and also includes a cheer, similar to those found in the S23 College Yell silk issue. However, that set included pictures of some generic athletes while this one does not, so a specific sport isn’t really identified in the set. However, many collectors associate college yell cards with the sport of football, so some may consider D96 to be loosely a football release.