PART VI. Striking Errors:

Saddle Strikes:

Sideneck Strike

Definition: A sideneck strike involves a collision between the unstruck edge of an off-center coin and the neck of the adjacent hammer die. During an off-center strike, the struck tongue of metal expands in all directions.  This expansion pushes the unstruck portion of the planchet sideways.  If it’s positioned just right, the pole opposite the struck tongue of metal will collide with the adjacent hammer die.

A sideneck strike leaves a smooth, curved indentation at the pole opposite the off-center strike.  This error is as close as you can come to a saddle strike without actually being a saddle strike.  Sideneck strikes often show a pattern of buckling identical to that of a humped saddle strike.

Other terms used to refer to this error include “almost saddle strike” and “one-die saddle strike.”
The Lincoln cent shown below shows an off-center strike in association with a sideneck strike. The characteristic concave facet is easily seen.