Although it is difficult to find sports related free images, you can with some effort find Creative Commons Images from two sources:

• By doing a google image search by using this search method:

"Google Image Search>>Your Search Term>>Tools>>Usage Rights>>Creative Commons Images."

If you are using this method be sure to check and verify that these images are indeed Creative Commons Images, before proceeding. Google does list commercial images (not free images) by error under that search. Creative Commons also has specific attribution requirement, which you must follow.

• From OpenVerse

Alternatively, design yourself a Sports Themed Banner as some bloggers are already doing for all their posts. If you are not good at designing then you could ask one or more of the bloggers in the Arts related communities for help for a small fee. You could submit a classified ad in the HiveList Classifieds Community and ask for help from these designers, tagging some of them you have already identified. One such person who could possibly help is @vickoly.

You can also search for these designers in https://peakd.com/created/diy.

Finally, as a last choice use copyrighted images if you are sure your use of the images falls within the ambit of Fair Use doctrine. If you use this method make sure you include the Fair Use Notice at the end of your blog post as mentioned in the Rules.