You've stopped the motion ok. This shot has some additional impact potential had you gotten lower to the ground, maybe include some foreground grass up close. Lighting is a little harsh. If you dropped the highlights a little, and brought up the midtones it might help (in Post-Processing). A polarizer would have helped this image and colors pop tremendously. All JMO of course. ;^) Good luck in the challenge.
you got the easy part of the swing...the challenge would have been to have stopped the motion at the point of impact. it's a beautiful shot, but as far as the challenge goes, i think you missed a real opportunity.