Why would a bike pedal backwards, but not forward? I found a bike in our junk pile and it caught my eye. So I decided to fix it up by putting a rear tire and a chain on it. Pedaling forward fails to move the rear tire, but I can freewheel backwards.

Why would this be?
There is likely something wrong with the rear hub, the bearings may have seized.

If you remove the wheel from the frame can you spin the wheel whilst holding it by the axle?