Explain a period on strike (5,3)
I believe the answer is:
spell out
'explain' is the definition.
(I know that spell out is a more specific form of the action particularise)
'a period on strike' is the wordplay.
'a period' becomes 'spell' (spell can mean a period of time).
'on strike' becomes 'out' (I've seen this before).
'spell'+'out'='SPELL OUT'
(Other definitions for spell out that I've seen before include "writing letters?" , "Give precise details" , "Temporary release from prison" , "Explain in detail" .)