It looks to me as if a wire, or string, was on the metal sheet as it was being rolled thin, thus leaving an incuse impression on the blank planchet. The coin was later struck on the resulting defective planchet. What are your thoughts?
Possible I suppose, looks more like a strike through to me though. edit - take a look at this one Jody. As you know I was never an error collector, but that doesn't mean I never owned any. This one was a strike through, a piece of string used to wipe a rusty die was the likely culprit, and it has many of the same characteristics as your coin.
It could be a strike-through or a lamination error. Hard to say given the resolution of the photo and the state of wear.
