What is a development league and why do I need it? A development league is a sports team that focuses on the player development of participating athletes. These are common for professional sports. The NBA's G-League is just that. Its formerly known as NBA Development League (NBA D-League). MLB has a tier for their development league- Triple-A, Double-A, High-A and Low-A . Development Leagues are a great way for athletes to be exposed to a higher level, learning more about the sport. It cultivates success & builds a winner's mentality. It is rare to see a local youth developmental league. Other countries have a higher value for this, offering them to the community often and early.