The Danish New Year's Eve custom of throwing old dishes at doors is known as plate smashing.
In the tradition, people save unwanted plates and other crockery, then break or throw them against the doors of friends, neighbors, or family members around New Year's. A pile of broken dishes outside a home is interpreted as a sign that the household has many friends and well-wishers. The practice is a form of noisy communal celebration rather than an attempt to damage valued tableware.
Reports describe the custom as especially associated with Denmark, although practices and popularity vary by place and generation. Modern celebrations may be more restrained because of safety, cleanup, and property concerns. It is therefore best understood as a traditional or reported Danish custom, not a universal rule followed by every household.
This practice is separate from the Danish habit of jumping from a chair at midnight, which symbolically “jumps” into the new year. Both customs can appear in accounts of Danish New Year's Eve, but the broken crockery identifies plate smashing.