I worked for an offset printing company for many years and believe that the back of the card was part of a full sheet that was used for Make-Ready purposes for the printing press. The pressman would get the press setup and run several sheets of paper through the press to prepare the press for the actual product.
http://graphicdesign.about.com/od/pr...make_ready.htm
Seeing how there are several different images on the back of this card, this sheet was "recycled" and used several times, rather than using all new paper for the make-ready process (no reason to use new paper when you can just reuse the scrap). There would have been more than one sheet used for this process and this one must have gotten mixed in with the actual press sheets or could have been used as a cover sheet for the cutters while trimming. Seeing how the front of the card looks to have a good appearance, my guess is that this make-ready sheet was accidentally mixed into the good cards. Most of the cards were probably caught by a packaging employee and this one slipped through somehow.
I would be curious to know what "other" products were printed at the same time as these cards, at the same company, using the same printing press or a sister printing press that could have possibly shared the same make-ready sheets. If we knew of other items that were printed at the same time, there could possibly be this same type of "error" on other products.
Just my thoughts.............
Also, the front side of this card appears to have some additional "yellow ink" on the lower left side, under the players foot. Does it appear to be that way through a loupe? Is this yellow ink a solid or does it have half-tone dots? I'm just curios if the front of the sheet was used as a make-ready for something other than a ball card.