A colloquial term in football for a hard, violent collision between two or more players on the field or a game that features especially intense or bloodthirsty competition.
The words that give meaning to the term "slobber-knocker"
indicate a hit or "knock" on a player that causes spit or "slobber"
to fly from his helmet. Over time the term has come to symbolize
any football contest that includes especially violent or intense
play between teams.
Games will sometimes be referred to as "slobber-knockers" by broadcasters or journalists when the contest has been characterized by rough play. As football is traditionally a violent sport, a "slobber-knocker" is a game that escalates this violence even further.