September Selfie No 22

I know, dreadful Selfie, but I need your help! !! I found this 'lump of lard' in the wooden planter behind me. Can anyone tell me what it is and how it got there? !
It's greasy and smells lardy. It was in a ball and covered in soil but perfectly clean and white inside, about the size of a large orange.

What the bloody hell is it!!!!!!!!

Thanks!