This is a 1991 Score "wrong back" error, with the back to a Jay Buhner card appearing in place of the normal Wallach card back. I remember these errors being somewhat common in the late 80's and early 90's. I never actually pulled one out of a pack, but just about every card shop I ever went in had at least one or two of these in there case. They used to demand a pretty high price, $10-30 if I remember correctly. This one didn't cost me much of anything. To be honest I don't remember how I came into possession of this, it was stuck in a drawer to be posted and forgotten about for the last year or so. It was either sent by a reader (sorry for not giving credit if that's the case) or bought for no more than a buck or two on ebay.
For book keeping purposes, I'm not counting this as a unique card, or towards the 1991 Score tally. I'm just deeming it another oddball collectible.