Neil is off course (4)
I believe the answer is:
line
'course' is the definition.
(I know that course can be written as line)
'neil is off' is the wordplay.
'is off' is an anagram indicator.
'neil' with letters rearranged gives 'LINE'.
(Other definitions for line that I've seen before include "Railway track; wrinkle" , "cover on the inside" , "(Skin) wrinkle; limit" , "Phone connection; queue" , "classified information" .)