It's now on the periphery of sporting awareness or interest, but there was once a time—and a very long time it was—when there was no bigger event in sports than a heavyweight title fight. And no bigger pay day. That's where taxes come in.
For a very long time, boxing was the only really big-money sport for athletes. Not for nothing did Marlon Brando's Terry Malloy regret taking the dive that cost him "the title shot outdoors in the ballpark" in On the Waterfront. At a time when Babe Ruth was being razzed for his $80,000 salary (more than the President of the United States, it was pointed out, to which Babe supposedly replied in 1930, "Well, I had a better year than he [President Hoover] did"), heavyweight champion Jack Dempsey made about nine times as much—over $700,000, for his unsuccessful title defense against Gene Tunney in 1926. And Tunney made $990,000 when he defended the title (and survived the infamous "long count") against Dempsey the next year. Between the two of them, they earned more than the entire 1929 payroll of baseball's American League in their two championship fights.
Where big money was being minted (and in full and very public view), the tax man inevitably followed. With no sadder result than the ordeal of Joe Louis.
[heartrending story followed by the prizefighting economics of the 90% tax band, Henry Fetter on How Taxes Changed Boxing, ht MR, ht Andrew Sullivan...]