Method 1: An off-center planchet can become trapped between the descending hammer die and a collar frozen in the “up” position.  As a result, the trapped planchet is sheared in two.  This is the most severe manifestation of a stiff collar error.  The portion of the planchet protruding outside the striking chamber becomes a curved (and often crescentic) strike clip.  The portion remaining within the striking chamber becomes an elliptical strike clip.  This form of elliptical strike clip is almost exclusively confined to copper-plated zinc cents produced between 1989 and 1994.

Elliptical strike clips of this sort are often mistaken for elliptical clips.  However, the two errors are easy to distinguish.  In an elliptical strike clip, the design at one pole (the pole next to the sheared edge) is always complete.  The face struck by the anvil die (usually the reverse face) has a rounded shoulder at this same pole and what appears to be an abnormally wide interval between the die struck design and the coin’s edge.  Opposite the rounded shoulder, the obverse face shows a vertical flange — metal pushed up by the immovable collar.  In copper-plated zinc cents, the zinc core is usually exposed where the coin was sheared in two.

This 1991 cent shows a typical elliptical strike clip with all the diagnostics mentioned above.  Coins like this are invariably and erroneously encapsulated as elliptical clips by the major grading services.

Method 2: An elliptical strike clip can also develop in the course of an off-center uniface strike.  When a planchet or coin is struck against another planchet, effective striking pressure is elevated as a matter of course due to the double thickness between the dies.  If ram pressure happens to be abnormally high as well, the portion of the planchet or coin trapped beneath the die and the second planchet can be torn off.  The resulting elliptical strike clip is very thin. These types of elliptical strike clips are often labeled as “struck fragments” by dealers and grading services.  But they’re really just pieces of “coin shrapnel” (bits of a larger planchet or coin that breaks off during the strike).