Moderate beheaded in many cases (5)
I believe the answer is:
often
'in many cases' is the definition.
(I've seen this before)
'moderate beheaded' is the wordplay.
'moderate' becomes 'soften' ('soften' can be a synonym of 'moderate').
'beheaded' means to remove the first letter.
'soften' with its first letter taken away is 'OFTEN'.
(Other definitions for often that I've seen before include "Frequently, at short intervals" , "Repeatedly with regularity" , "Turn away" , "In many cases" , "Commonly" .)