Yes, that is a large portion of the reverse of a 1951 Topps Team card! This particular oddity was likely produced during the second run of Red Backs and Teams, where brilliant white stock was used (the first run was cream for both sets). I believe this would mean the Team cards were of the undated variety, the 1950 dated versions coming last since they only come on brilliant white stock.
So what to make of this monster? Well, I think it means the Teams, which were on the same sheet as the Connie Mack All Stars (see the miscut below to see how they were next to each other on the sheet), but probably not the Red Backs, had been run off first.
My initial operating theory is that the red ink for the Team cards, which is the same as used on the Red Backs, was run off on a couple of Red Back sheets as a color test, then put aside to be used to used with other waste sheets as protection on the tops and bottoms of each stack of uncut sheets as they were palletized and banded for transportation from the printer in Baltimore to Brooklyn. I still think that latter part is correct but am rehthinking if all three sets were on the same sheet since they were sold together as Baseball Candy in 1951
The orientation is right I think when my miscut backs are compared to Connie Mack above- printed to the side and not atop a Team card.
I have never seen anything like these two Red Backs and wonder if any more are out there. I started a thread on Net54 about them as well, which may be worth checking in on. Hopefully more information can be developed.