I suspect you'll get a lot of comments about this being side-lighting rather than backlighting but it's just a matter of a few degrees variation in viewpoint and I tink it's a strong image, really nicely done.
DNMC
the subject must not become a silhouette because of the backlighting.
Since you commented I will elaborate more on why I am saying what I am about this. areas of the subject to my eye have no detail other than an outline Hence "Becoming a silhoutte". Also the lighting appears to be coming from your subjects hands and he is turned slightly away from the camera, this seems to be more like side lighting than back lighting. There is light cast on the background but really does not draw your attetion to or help the background.
While I do not think this image meets the challenge I do think it is a wonderful work of art with alot of emotion and detail the texture, tones and focus are very good. I think if the rules for the challenge were diffrent that this shot would score much better as it is very nice. Even adding as a fave as the shot is that quality even without the challenge credentials.