Found sailor lying in street (5)
I believe the answer is:
start
'found' is the definition.
(as in to establish)
'sailor lying in street' is the wordplay.
'sailor' becomes 'tar' (tar is a kind of sailor).
'lying in' is an insertion indicator.
'street' becomes 'st'.
'tar' put into 'st' is 'START'.
(Other definitions for start that I've seen before include "Beginning" , "Begin; flinch" , "get under way" , "Origin" , "begin an argument?" .)