The Astros have attempted to sign minor league players to long term deals in the past, such as George Springer, but have never succeeded. Obviously, they want to do this so that the player would be willing to take a lower contract offer so he feels more secure if he cannot make the major leagues. Singleton's deal is the first of it's kind - no player in the history of baseball has signed an extension like this with absolutely zero major league service time.
Singleton, the Astros number six prospect by Baseball America, has spent this season with Triple-A Oklahoma City. Since being drafted in the eighth round of the 2009 MLB Draft by the Phillies, Singleton has had his ups and downs. He was suspended back in 2013 for his second violation of baseball's drug policy. However, over his professional career thus far, Singleton has hit .279/.388/.466 with 75 home runs and 318 runs batted in over 2260 plate appearances.
Jon Singleton does a good job of using the whole field and has a chance to become a .280 hitter in the major leagues. He is prone to strikeouts and isn't fast, but does a good job of driving the ball, which could translate to 25 home runs in the big leagues. He's improved this season, posting a .267/.397/.544 line with 14 home runs and 37 RBI in 239 plate appearances.