Keep reading Grantland. They have great weekly columns, particularly for the NFL and NBA, that have broadened my understanding for and appreciation of the sports I thought I knew. Honestly, they're the best.
You could also try fantasy sports, but they don't teach you much about the game - they just encourage the sort of singleminded obsession that makes learning any subject easier.
You could also try fantasy sports, but they don't teach you much about the game - they just encourage the sort of singleminded obsession that makes learning any subject easier.