The term "bush league" has a literal meaning as well as an idiomatic meaning. It originated as a term for minor league baseball, which is often played in rural towns that are sometimes referred to as "the sticks" or "the bush." The term "bush league" has come to refer to anything that is considered amateurish in nature or of lesser quality, rather than being of the highest professional quality.
Minor League Baseball
Early in the development of baseball as America's national pastime, particularly in the early 20th century, the sport was played by minor league teams in many small towns across the United States. The leagues in which these teams played were often referred to as bush leagues. Unlike much wealthier major league teams, minor league teams often operated on very low budgets, especially those that were not affiliates of major league organizations. Although these were professional teams and players were paid for playing, the perception was that they were somewhat amateurish.
Another aspect of minor league baseball in those days was desperation on the part of the teams and the players. Bush league teams were often desperate for fans' attention, and their players were desperate for attention from major league teams. This desperation often resulted in extreme actions or even gimmicks that likely would not take place in the major leagues. For example, bush league teams might hold unusual promotions or stage publicity stunts to draw fans to their ballparks. Players might try to bend the rules to gain an advantage and make themselves seem to be better in comparison with other players.
"Bush league" is often used as a derogatory term in everyday speech, usually as an adjective. In some cases, this term implies that something is substandard or inferior. A business that lacks professionalism, for example, might be referred to as a "bush-league operation." At other times, it is used to describe an action that is considered unprofessional, gimmicky or perhaps even unscrupulous. An action that benefits one person at the expense of another might be called a "bush-league move."
A shorter version of this idiom is simply "bush." For example, someone might refer to a particular action by saying, "That's bush." The meaning is the same — the action is being called unprofessional, amateurish or unsophisticated.
Use in Baseball
Although the term "bush league" is often used as an idiom in many contexts outside the sports world, its most common usage might be in baseball. It is often used when one of the so-called unwritten rules of the game is violated. These are rules of etiquette that typically are followed by teams during baseball games at all levels. Trying to surprise the opponent with a "hidden ball trick" or bunting to try to break up a no-hitter in the final inning, as two examples, might be called bush-league plays whether they take place in a youth league or in the major leagues.