Boxing and wrestling (and baseball) were hugely popular spectator sports at the time this short was released. Professional football, hockey and basketball were still in their early stages of development.
Daffy Singing Sinkin In The BathTub Is A Reference To The First Looney Tunes Cartoon Sinkin In The Bathtub (1930)
Daffy's "Sold to the American Tabasco Company!" is a parody of the American Tobacco Company's "Sold American" auctioneer ad for Lucky Strike cigarettes.