King Charles in total struggle (5)
I believe the answer is:
scrum
'struggle' is the definition.
(I have seen 'Disorderly struggle ' mean 'scrum' so perhaps 'struggle' could also mean 'scrum')
'king charles in total' is the wordplay.
'king charles' becomes 'CR' (Carolus Rex - King Charles in Latin).
'in' means one lot of letters goes inside another.
'total' becomes 'sum' (synonyms).
'cr' put within 'sum' is 'SCRUM'.
(Other definitions for scrum that I've seen before include "group of forwards" , "Feature of rugby match" , "Scrimmage" , "Rugby gathering?" , "Rugby-players crouch here" .)