It's either strike doubling or die deterioration doubling (or a combination of both). In either case, it's worthless.
Can you post a picture of the entire coin? 1983-P quarters in decent condition are collectable in their own right due to poor quality control that year. Do an ebay search for an unopened 1983-P roll of quarters and you'll see what I mean. If there are any available, it will probably be going for something in the $400 range.