Time to get behind former leader and Chief Justice (4)
I believe the answer is:
taft
'former leader and chief justice' is the definition.
(US president and chief justice William Taft)
'time to get behind' is the wordplay.
'time' becomes 't' (abbreviation).
'to get' means one lot of letters go next to another.
'behind' becomes 'aft' (synonyms).
't'+'aft'='TAFT'
(Other definitions for taft that I've seen before include "former President" , "27th President of the United States" , "US president, 1909-13" , "US President before Wilson" , "27th US president, William" .)