Police came to rally (3)
I believe the answer is:
met
'police' is the definition.
(London Metropolitan Police)
'came to rally' is the wordplay.
'MET' is hidden within the letters.
However, I'm not sure how this is indicated.
Can you help me to learn more?
(Other definitions for met that I've seen before include "Came across - police in London" , "Encountered or touched" , "Encountered pro tem" , "Opera company" , "Came together, encountered" .)