After 18 years, Smith joined the New York Herald Tribune. He cemented his reputation with the Herald-Trib, as his column was widely read and often syndicated. When the paper folded in 1966, he became a freelance writer. He joined The New York Times in 1971 as a contract writer. By this time, his reputation was secured as one of the foremost sportswriters in America.
Smith is one plausible source for the quotation, "Writing is easy. You just open a vein and bleed." In 1946, sportswriter Paul Gallico wrote, "It is only when you open your veins and bleed onto the page a little that you establish contact with your reader." In 1949, columnist Walter Winchell wrote, "Red Smith was asked if turning out a daily column wasn't quite a chore. ... 'Why, no', dead-panned Red. 'You simply sit down at the typewriter, open your veins, and bleed.'"
Smith was a strong critic of former world heavyweight boxing champion Muhammad Ali until late in Ali's career. When Ali refused to serve during the Vietnam War, claiming his case as a conscientious objector, Smith (who had never entered military service) wrote: "Squealing over the possibility that the military may call him up, Cassius makes himself as sorry a spectacle as those unwashed punks who picket and demonstrate against the war", and berated Ali for being a "draft dodger" and a "slacker".
Later Smith famously commented on Ali's first professional defeat in 32 bouts, against Joe Frazier: "If they fought a dozen times, Joe Frazier would whip Muhammad Ali a dozen times; and it would get easier as it went along". Ali went on to fight Frazier twice more, winning both times, once by unanimous decision and once by TKO. Before their final match, the 1975 Thrilla in Manila, Smith admitted Ali was both a great fighter and a great man.