Healthy hens, primarily on there younger years, will occasionally lay a misshapen egg here and there but not on a frequent basis. In this post, I will explain some of the causes of Smashed-in eggs (which are called slab-Sided eggs) and White-banded eggs. . .
Slab-Sided egg (as pictured above). The Main Causes: Drastic lighting changes, Over-crowding and/or stress. Slab-sided eggs can also be an indicator of illness but I have had perfectly healthy hens in my flock lay them so a one time occurrence is nothing to be overly concerned of.
How it happens: When two eggs enter the shell gland pouch (one shortly after the other), the second egg, being not as complete as the first, flattens on the side where the two eggs make contact. The same thing occurs with White-Banded eggs (pictured below) except with white banded eggs, It is the calcification process that is interrupted by egg shell contact, making an extra deposit of calcium.
Above picture borrowed from BackYardChickens.com