While researching another topic, I noticed this detail in an engraving after John Collet's An Holland Smock to be Run For:
1770 - Lewis Walpole Library
It led to some research that first taught me that a flitch is a side of bacon and second that there were some unusual contests at fairs and other celebrations in the 18th Century.
American Notes and Queries, Vol. 3, 1889 - Wm. H. Garrison
referencing a 1776 handbill
Digging through flour with your mouth sounds just awful, and possibly smothering. I imagine there was a lot of coughing involved.
Wit, Character, Folklore and Customs of North Riding
of Yorkshire, 1898 - Rich Blakesborough
The most surprising thing was not that sack races had been around for so long,
