The call it the Law of the Ex.
It dictates that when a sportsman meets one of his former clubs he always manages to cause them some pain.
This weekend Serie A has such prospects in spades.
It would be a huge suprise if Livorno's Nelson Rivas (pictured) did anything to harm Inter Milan. Indeed (his former employer), he probably gave them more trouble when he was playing in their black and blue colors.
There are others, however, who could do more damage on Saturday and Sunday.
For five men in particular it will be a time to confront their past and hope to come out on top.