Sauce boat not completely put back (7)
I believe the answer is:
ketchup
'sauce' is the definition.
(I've seen this before)
'boat not completely put back' is the wordplay.
'boat' becomes 'ketch' (ketch is a kind of sailing vessel**).
'not completely' means to remove the last letter.
'back' says the letters should be written in reverse.
'put' with its last letter taken off is 'pu'.
'pu' back-to-front is 'up'.
'ketch'+'up'='KETCHUP'
(Other definitions for ketchup that I've seen before include "Thick sauce, with tomatoes" , "Piquant sauce, often tomato based" , "Sauce made largely of tomatoes" , "Relish" , "Red sauce" .)