It looks like a zucchini.

That's what I thought by the look of the leaves, but if it is zucchini, it's already the fattest and oddest shaped one I've ever seen. Not that I'm an expert, but it sure doesn't look like the zucchinis in the store.

Zucchinis will get quite big if you let them (much bigger than at the store) and it is not that unusually for them to have a larger end and not be uniform all around.

The fruit and the leaves look like zucchini leaves, but the best way to tell would be to cut it open and try it. It could always be some hybrid of a zucchini and something else.

If it is a bush type squash without long vines or tendrils I really think it is a zucchini.

I think you're probably right. Now I know I can pick them soon, unlike some sort of winter squash. Thanks for the help.

Several of the grey type zucchini have this club shape, not unusual at all.