This is wonderful! What you could do is assure the file is named 'jpg' and not modified to 'JPEG' during your processing. With the more universal file extension, the thumbnail will appear for the attachment when posted to UHH. (You have nearly 60-minutes after creating a post where you have access to an <Edit> button where you can remove this attachment and add another as a replacement.)

You might also crop this image much closer, placing the athlete to the left 1/3 vertical of the frame (from the near center position of this version) and placing the names of hurdles along the lower 1/3 guide line. This would remove all the background, simply through elimination. Use a 'modern' 16:9 aspect.

If repeating, I'd simply repeat this image, trying to capture the full image closer to the suggested crop above. You'll likely need to stand closer rather than extending the focal length, maybe both. Will the evening light shine into his eyes? Can you go manual with the same aperture, but force a faster shutter, even is just to 1/640? Do you have a single point or small group focused on his face? With the plan to position the athlete to the left within the frame, position yourself, your camera / tripod, and the AF point all to the 'left' to capture the image in the camera closer to the intended result. If the athlete is willing, work this shot repeatedly at different apertures. If you can hit his face in perfect focus, I'd be interested of the results at f/5 rather than f/9 of this version, another effort to minimize the background in a more artistic way.