mine do this so i went and researched goldfish breeding and apparently they can get quite rough with the male literally pinning the female to the floor/rocks/sides etc. personally i think the nudging thing is just normal behaviour.
found this:
Goldfish and Koi have very "active" sex lives. To put it in laymen’s terms, the male chases the female in a rather brutal show, literally to beat the eggs out of her. Then he fertilizes the eggs. Many times you will notice several males "courting" one female. This can be stressful to the female and can be a cause of injury. Many females, frantic to get away from their suiters, jump during this time and injure themselves against rocks or simply jump out of the water and onto the ground.
Mating activity usually happens whenever the water heats up rapidly and is more apt to happen in the morning and evening hours. If you wake up to find your pond full of white foam chances are your fish have been "up to no good". The white foam is a by-product of their escapades.
