In the United States I would have to say Baseball was the most popular sport. It had been running strong since the 1920's. The teams of the 50's were huge. Take your pick... The Brooklyn Dodgers with Jackie Robinson or the Yankees, Red Sox, Cubs, etc. The NBA, NHL, and NFL/AFL were all around but none of which could compete with how big hardball was at the time. It's not called America's past time for nothing.
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I think you can answer that yourself, by asking "what new sports are there that have been invented since the 1950's. All the ones that were popular in the 50's are still popular. Baseball, Football, and Basketball were the big three. In America of course, Soccer has never been particularly popular, but has enjoyed a bit of success too. Nascar started in roughly, 1950, and has enjoyed a lot of success since. Other than that, I don't know what to tell you.
Willie Mays, Mickey Mantle, Rocky Marciano, Patterson, Sugar Ray Robinson, Jimmy Brown were the most popular.
American football and baseball were huge. Soccer was on the rise, but would take a while to grow into what it is today.