I thought the long pink balloons (see picture) at a baseball game on Japanese TV was just for the visual effect and waving back and forth, but no : at a given signal everyone let go and up and away the balloons went, and plopped (deflated) back onto the spectators – that was part of the fun. Baseball is very popular but not the national sport (sumo wrestling is). of the league can be traced back to the formation of the “Greater Japan Tokyo Baseball Club” in 1936. (In the USA, Major League Baseball traces its history back to 1869, the year the ‘Cincinnati Red Stockings’ was established as the first professional team).
The teams all have their fan clubs and websites and each team is a franchise that endorses or markets all kinds of products and events.