Great pic and decently sharp. You must have been very close to get this with a 300mm lens.
Sharpening (either in-camera or in post processing) has created a coarse grain in the out-of-focus area behind the subject. This would look better (and enlarge better) if it were creamy smooth.
In my bird and wildlife pics I generally remove all sharpening applied by the camera and then mask the subject and apply sharpening only to that mask. This way, only the subject is sharpened. I use Nikon Capture NX2 but the same can be done in LR.
I am not sure if LR will allow you to edit the picture profile to remove sharpening applied in-camera. If not, you can do it by editing the picture profile directly in the camera (shooting menu). Rather than editing the existing profile, create a new one with your adjustments in it.