First impressions are of an appealing subject reasonably well captured that I hope fits the challenge.
As a keen cycling enthusiast I am always attracted to bikes particularly action shots. Your panning action has captured the cyclist nice and sharp and introduced a little motion into the background. This is where the problem lies for me, because of the high shutter speed there is not enough motion blur in the background it looks more like camera shake, thereby significantly reducing the appeal of the shot.
The other big problem is that you have a dark clothed rider caught in the dark shadow of a tree and with the shadow unfortunately falling right across his face, probably the most important part of the image, the part where we can identify with the moment he is experiencing through his facial expression. Also the composition, I'm not sure why you feel the portrait orientation works better than landscape but I am all for a non-standard approach as long as it works. Because of the size of the rider and the amount of space he has left to ride into it probably just about works.
'I hope it fits the challenge', I am unable to judge this as I don't know what Ubique's philosophy is but I do like his comment, perhaps I am missing an important clue to that in his comment? I have followed the challenge description which has a link to a forum thread where I was hoping to learn more about his philosophy and try to work out whether this does fit the challenge, with 3760 comments to review I'm afraid life is just far too short, sorry.
What comes to mind here is "looking for Sasquatch". The rider looks out of place and lost as there is no visible trail. Nice flux between light and shadow.