KWED
Scratching head, scratching knee
In his tafsir, Ibn Kathir describes "fasad" to include "disbelief and acts of disobedience to Allah's law". That seems to cover just about everything!I agree. In most of the Qur'an's 50 references to fasad, it seems to be understood that we already know exactly what that entails.
I think the clearest definition comes from 16:88 - "Those that disbelieve and bar from the way of God -- them We shall give increase of chastisement upon chastisement, for that they were doing corruption."
Even without that verse, the fact that the entire qur'an is dedicated to defining the difference between Islam and any form of infidelity tells us that Fasad refers to anything disapproved of by Allah. Claiming that God had a son would be an obvious example.
And we know that 5:33 prescribes execution by torture as an appropriate punishment for "fasad".