The leaves and tendrils look cucumber-ish. I say it's a cucumber. Sure doesn't look like a pumpkin.

What is the cultivar?

What is the seed source?

kimmq is kimmsr

Which plant is it on? Cukes and pumpkins don't cross pollinate.

perhaps a cuke that didn't get well enough pollinated to get full size? Some of my snake gourds would do that - be ball-shaped stead of snakey

It is just a mongrel cucumber. The seed was in the packet you bought (or in the packet your grower bought). It happens often with cucurbita, and it has happened to me several times with squash, melon, and once with cucumbers.

Here's a newer pic. Anybody recognize it?