 Thus, the need to use ballparks played a large part in ensuring that the National Football League and early rivals would delay the start of their seasons until September when the baseball season was winding down, thus affording baseball teams the exclusive use of their facilities in the spring and summer.Starting in the 1950s, a number of technological changes and trends eventually caused some to question the traditional timing of the American football season.In particular, football became a much more lucrative sport, the invention of artificial turf and developments in the growth and maintenance of natural grass made it more practical for baseball and football to be played at elite levels in the same facility at the same time, and the increasing influence of television combined with the prevalence of a farm system in which Major League Baseball controlled the rights to baseball levels in all levels of play caused many minor league baseball clubs (some of whom played in large facilities that could be easily re-purposed for major league football) to be much less lucrative in their own right.