A while back, when I was doing some research and going through some newspapers of the 1920s and 1930s, I was struck by how sports coverage was dominated by baseball, boxing and horse racing. Football, basketball, and other sports were just footnotes. Local newspapers even had "late racing editions", late-night editions published after all the results from tracks in the Northeast had arrived. This was in the days when "off-track betting" meant "bookies". (I believe a couple of newspapers in the NYC area still have late racing editions.)
Today, boxing and horse racing still have their fans, but they're nowhere near as dominant as in the pre-WWII era. Today, the "big four" major sports in the United States are football, baseball, basketball and hockey. Do you think there will be a time when any of those sports fades into the background much like horse racing and boxing did in the past? What will replace them?