One thing that helped my sports loving son (and his older brother, who also loves sports) was the desire to read the sports section of the newspaper. My first grader gets the sports section in the morning before anyone else and discusses strategy, teams, players, my DH's fantasy teams, etc. It's really helped with his reading. He knows the line-up of pretty much all the pro basketball teams and is pretty good with the baseball and football teams, too. And those words/names are a heck of a lot harder than the words in a first grade reading books.
Take something that your son loves and go with that. It gives a purpose to reading, too.