Circling back to my original comment ... OF COURSE you need to get an OK from your current shop to do this side hustle.You absolutely do not owe your shop any content you produce on your own time. It sounds as if you are no longer involved with sports coverage, so there should be no conflict of interest in taking on sports freelance assignments.
That said, I'd get an OK to be sure.
This goes without saying, but if you run it by your bosses and they try to twist it into, "Well, if you're going be doing that stuff anyway for them, can you tweak it a bit for our readership so we can use it?" ... that's a non-starter (unless they're going to pay you beyond your current salary).