It was not over a political difference. The Who were there to perform, not listen to Hoffman’s crap.
The dialog went something like:
Hoffman: “I think it’s a pile of s*** that John Sinclair rots in prison.”
Townshend makes an inaudible comment; Hoffman responds with “What?”
Townshend, clearly audible: “Get the f*** off my f****** stage!”
Watch/hear it til the end. It’s only 1:18 mins.
The Who - Abbie Hoffman incident - Woodstock 1969
https://www.youtube.com/watch?v=Q8BYgzIEHIY