I took rear wheel off to fix a flat and now mower won't move?

If it was on a shaft with a keyway to lock the rin to the axel, did you foregt to put it back in or did it come out by accident when being put back on.

That type would have a single nut attaching the wheel to the axel.

If you have the type bolted to a hub with 3 or more lug nuts or bolts it will be something unrelated to the flat tire.

That's what it was, thanks!