I would narrow it down just a bit. Start with one sport for example : foot ball. could you write about foot ball ? you can add in other sports later.

Sports is a great niche, however broad.

You need to discuss a focused aspect of sports to a qualified group of people who would be your target audience (that could be beginners or another group you have in mind), you would help people by giving them advice, walk them through your journey and then promote products however relevant.

Hi mr kyle im a little bit confused with this niche thing. I am choosing my "audience" as all sports