Yeah, it's not grease or glue on the coin. The metal is pushed back toward the lettering resulting in a trough between the lettering and the rim below the surface of the coin. Maybe just an irregular struck though or defective planchette. I have another state quarter (Virginia) with the same error.
Thanks everyone for all their input. Much appreciated!
Thanks for the info. Do you know where I could find a reference to a Die event due to worn anvil? I couldn't find anything on error-ref.com. What's the main differences or key indicators between the die event and the spitting horse error? Again thanks everyone for all the feedback.
I found a spitting horse die crack Delaware state quarter. However, it's on a Denver minted quarter. I can't find any other examples, just the more common Philadelphia errors. The die crack is in the same position as the Philadelphia examples. Has anyone saw a 1999D spitting horse?