'Five Go Off To Be Sick'? Leave it out! (4)
I believe the answer is:
omit
'leave it out' is the definition.
(I've seen this before)
I cannot understand how the remainder of the clue works.
(Other definitions for omit that I've seen before include "Leave out or undone" , "Drop" , "Fail (to do something)" , "Exclude - neglect" , "Miss out" .)