Pursuing legal action, conforming with what another has done (9,4)

'pursuing' is the definition.
Although both the answer and definition are present participle verbs, I can't understand how they can define each other.

'legal action conforming with what another has done' is the wordplay.
I cannot really understand how this works, but
'action' could be 'following' (following is a kind of action) and 'following' is found in the answer.
'done' could be 'u' and 'u' is found within the answer.
The remaining letters 'sit' is a valid word which might be clued in a way I don't see.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?