I found a link from AS and they confirm that he said to the ref "la puta madre que te pario". There's no "I shit on", it's simply because in English you have to be very specific about what you say whilst in Mediterranean euro-languages you can say a phrase without half the words and everyone understands it and its context. Heck, we can communicate without even saying any words but just making random sounds
and hand gestures
It translates to "the whore mother that gave birth to you". But the 'gave birth' part is really vulgar, it's not the decent way of saying a mother gave birth, it's like she shat the child, which a) it's why it is offensive and b) why the English translation has created the phrase "I shit on" just to provide enough context of what was said.
It's extremely common in Argentina and the Americas in general, but I haven't heard it so much from mainland Spanish people though. The Argie refs react very lightly to it, the Spanish guy was either looking for an easy reason to send him off or was geniunely offended by it.