Crossword Genius

Penultimate part of Shakespear­ean play is beginning to move into vigorous campaigning (8)

Ross

I believe the answer is:

'vigorous campaigning' is the definition.

'penultimate part of shakespearean play is beginning to move' is the wordplay.
'penultimate part of shakespearean play' becomes 'activ' (fourth of five acts in a Shakespeare play).
'beginning to' suggests taking the first letters.
The first letter of 'move' is 'm'.
'activ'+'is'+'m'='ACTIVISM'

'into' is the link.

(Other definitions for activism that I've seen before include "Political efforts", "Policy of vigorous work as in politics".)

I've seen this clue in The Guardian.