Leave some lettuce on? No (4,3)
I believe the answer is:
head off
'leave' is the definition.
The definition and answer can be both to do with social activities as well as being verbs in their base form.
Maybe they are linked in a way I don't understand?
'lettuce on? no' is the wordplay.
'lettuce' becomes 'head lettuce' (head lettuce is a kind of lettuce).
'on? no' becomes 'off' ('off' is the opposite to 'on').
'head'+'off'='HEAD OFF'
'some' is the link.
Can you help me to learn more?
(Other definitions for head off that I've seen before include "Forestall" , "like Robespierre?" , "Escape" , "Avert; start (in a direction)" , "Stop" .)