Shot clock

The NBA introduced the shot clock in 1954. Each team had 24 seconds to put up a basket if they did not then the other team gained possession of the ball. The shot clock allows the game to speed up and make it look more interesting. It also allows the players to run up the court and make plays, think fast. This lead to fast breaks, which I'm sure was interesting for the fans. Furthermore, the shot clock allows to play aggressive and get steals and as well as turnovers.

http://www.livestrong.com/article/350688-how-did-the-game-of-basketball-change/