Arrest leaders of those on strike (3,4)
I believe the answer is:
run into
'strike' is the definition.
(I know that strike can be written as run into)
'arrest leaders of those on' is the wordplay.
'arrest' becomes 'run in' (I've seen this before).
'leaders of' indicates taking the first letters.
The first letters of 'those on' is 'to'.
'runin'+'to'='RUN INTO'
(Other definitions for run into that I've seen before include "Happen to meet or collide with" , "charge?" , "Meet (a person) by chance" , "Come across, encounter" , "Encounter by chance - or collision?" .)