Catfacing usually happens to large tomato varieties like Beefsteak, Big Beef, Brandywine, and Cherokee Purple. Although catfacing can cause a tomato to be rather unsightly, most times it is harmless and the tomato can still be used. The larger one in my photo can not be used, as it is also developing blossom end rot.
Catfacing is caused by a drop in temperature when the tomato plant blooms, or begins to set fruit. It can be very difficult to control tomato catfacing since it is dealing with temperature. Brandywine tomatoes are one of the most difficult tomato varieties to grow, and catfacing is one of the most common problems. All I can do to prevent this is pick the catfaced fruit, and hope that I’ll get regular ones now that the weather has settled a little.