What is a mud run? I guess it's about running in mud. Seems to be a fun event.
I think it's great shot. The boy looks a little exausted which is probably why he is taken a break from running.
I like how you've separated the background from the boy using a low aperture. Works great.
Hi Melissa! I like the DOF here. I'd like to participate in this annual mud run sometime :)
TFS and welcome to TL!