So if I wanted to report news on Maria Sharapova or make a comment about her, would using an image from her official website be ok if I simply attached a link back to her site
I think this would be fine as you'd be covered by fair use.
However, a nice thing to do is simply email the websites of any people whose photos you want to use, and ask their permission.
If your site is all set to go so that you can send them the URL, so that they can see what you're doing with the photo, 99 times out of a hundred they'll say, yes, sure.
You might even be able to establish a rapport with the site developer and through them the athlete, who might give you exclusive news for your site. Okay, that might be a stretch, but anyway, they'll appreciate that you asked...