Anything amateurish or otherwise below professional caliber. Baseball teams have been divided into two broad categories. Major league teams, also known as the big leagues, have the most professional players who play in state-of-the-art stadiums. Then there are minor league teams, composed of players on their way up or down the baseball ladder and ballparks that range in quality from almost-major league to close-to-sandlot. The latter fields, especially those in rural areas, weren't always enclosed by fences; instead they had shrubbery around their perimeters. Hence the phrase “bush league,” where the level of play was far from major league ability. The expression quickly spread to any endeavor that was less than expertly done.