Hmmm, this shot gives me ideas. I love when a shot does this. With a long focal length, an extremely long exposure (5 seconds or so), and keeping the panning on the cart the whole time I bet this would be tremendous. High speed background motion, perfectly focused cart, blurrly legs.... I might have to try this. Probably take a few hundred shots to get the cart in sharp focus for that long of an exposure. Three different senses of motion. A little off the critiquing really but just rambling things as they come to mind...
Great ideas come from the simpliest photos.
As for the photo itself in this challenge, I think it was a great idea just a bit hard to sell to the motion panning voters. Exposure was good, angle was terrific, and the technique of panning was strong (but short lived).
Looks like he's having fun! :) I like that you thought of a different subject from the dozens of bikes and cars. I think with a little more "zoom" in the man, you'd have done better. Like had him bent over making "vroom" noises and running instead of walking. Compositionally, it'd be better to give him a little more room above his head. I like that you got down to the level of the cart and shot up at him, though.
I wouldn't say that pushing a grocery cart is the most exciting motion panning subject but you got the idea right. You might consider a longer exposure time to show more background motion in the capture. That is a key to great motion panning imagery.
Once again wheres the motion panning... SOrry to be mean but let me guess u tried it in auto? Try slowing the shutter speed a bit to capture more background motion.