It looks as if the coin took a hit on the 8, but I don't think it's an error, just Post Mint Damage otherwise known as
PMD. The reason I say this is the overall condition of the coin, I've never see an 1879 with a with an error like this on the date and the full outline of the 8 is still visible in the background.
I could be wrong, but I see damage, not an error.