1. To tour (rural districts), giving theatrical performances of a popular kind. - OED
The term "barnstorming" was used frequently in the early part of the 20th century with regards to itinerant baseball teams, especially Negro League
teams. Every summer, players not quite good enough to make (or not allowed to play in) the major leagues would tour the country, playing local business and semi-pro
teams. In the winter, it was not uncommon for major leaguers to join in, barnstorming and spreading the gospel of baseball
Before the advent of television, watching barnstorming teams was the only way many Americans could see professional baseball players. Thus, a contest featuring a popular barnstorming team in a small town could draw as many fans as many major league games.
Major League Baseball also undertook a number of barnstorming tours in the offseason to foreign countries, teaching the game and generating goodwill. A series of such tours to Japan in the early 1930s including Babe Ruth, Lou Gehrig, Jimmie Foxx and Lefty Grove were very popular, and led to the rapid expansion of Japanese baseball.
Barnstorming was an integral part of the Negro League teams; seasons would generally last less than 100 games, leaving the rest of year for teams to travel the country, playing unscheduled games and earning as much or more than they earned during the regular season. One of the best known barnstorming teams was the House of David, a team founded by a Michigan religious community; known for their long hair, beards, and proselytization.