The aggressor
There is a principle in law - i.e. one who hits first, he is responsible even for his own broken neck and the bleeding nose.
Habib Akram is right in saying - Imran Khan always takes the initiative to inflict unsuitable, unfounded, misplaced personal and political blows particularly on PML(N).
It is quite natural that a response from the opposite site is bound by certain limits and when an aggressor like Imran Khan trangresses such limits, there is bound to be a reaction