in hand at an angle you can see 1976 date but note how CRISP the back is proving no vice or other pressure device was used other than the mint. (vice or hammer would leave a flattened mark over the entire reverse of the coin no matter what padding you used IE: rubber tire, leather strip, cloth all would cause a flattened surface if pressure is on the obverse. (try it with YOUR vice... experiment with it)
There are several possible diagnoses: (1) a 90% "indent" (indentation from an unstruck planchet); (2) struck through a partial (off-center) uniface die cap; (3) struck through an elliptical clip planchet (possibly split or rolled-thin). The sharp internal margin suggests that scenario no. 3 might be the correct one.