Upload & Sell: Off
It's a bit hard to C&C these because this isn't a regular 5k. The costumes are a big part of the image. That said, I think the images are good not great, but if I'm honest, I don't have any specific suggestions for making them great.
Most of the photos are backlit and that can make some photos dramatic, but a little goes a long way IMHO. I also am not a fan of the post production. Colors look off and some images are muddy.
Shooting running is tougher than it looks. Yes, it's relatively easy to get a competent image. Getting great images are tougher. In non-costume races I tend to like the images that are cropped tighter. Some people like to see the runner head to toe, but IMHO they tend not to have impact unless there is drama in a pack
So, all that said, I think they are good images, but they just don't excite me to be honest. I think with some color correction and contrast improvement, some of the backlit images could be more interesting.
I shoot several running races and triathlons a year (purely for my enjoyment) and it's hard to be fresh each time. Sometimes I get images I really like, but I find when I try to get the same thing again (and do usually) a lot of times the images don't excite me anymore because I've already done that. Watch your backgrounds and lighting and try to get different perspectives. Unless you're just mass shooting to sell to the participants (which I find are 95% uninteresting), try to ensure your photos don't all look generally the same.
Sorry to be long-winded. Running is a passion of mine as a participant and I usually don't care for the images from the contract photographers. I try to do much better when I shoot my friends. As a parting note, by far the greatest image of me at Ironman was a highly amateur shot of me in the finish chute with a long enough shutter to have some motion blur, but bright enough strobe to freeze part of the image. Usually I don't like images that are shot from behind, but everything put together, the image captured the kaleidoscope that the chute turned into for me. It was an image I'd never attempt to capture (nor would most people), yet it worked incredibly well. I have a 13x19 to go on my wall. I bought the official photos and they will go on my wall as well, but this amateur image is my favorite. Try to be different from the usual "stock" photos.