Flailing sword around in royal house (7)
I believe the answer is:
windsor
'royal house' is the definition.
(Windsor is an example)
'flailing sword around in' is the wordplay.
'flailing' indicates an anagram.
'around' is an insertion indicator.
'sword' is an anagram of 'wdsor'.
'wdsor' going around 'in' is 'WINDSOR'.
(Other definitions for windsor that I've seen before include "Queen's Berkshire residence" , "Royal house (or castle)" , "somewhere in Berkshire" , "Type of soap" , "9 [HOUSE]" .)