I find this photo to have a major clarity issue. I believe its caused by the brightness and contrast level. Try bringing down the brightness by -5 or -10 and uping the contrast by +5 or +10. I think you'll find a more vibrant photo with less blur (I'm not refering to the background or the horses legs). Good luck in this challenge. <5>
nice capture. just a hair overexposted. just a personal perference but i would have liked the blur on just the foreground or the background. i'm thinking bluring the background while keeping the horse more in focus with a pan would have worked the best. perhaps you tried that and it's easier said than done as the feet move faster than the body. so maybe concentraiting on the head would have been easier. just some thoughts from someone who has never tried this technique and needs to do so before posting comments.