Knocking down protest hero full of appeal (10)
I believe the answer is:
demolition
'knocking down' is the definition.
(I've seen this before)
'protest hero full of appeal' is the wordplay.
'protest' becomes 'demo' (demonstration).
'hero' becomes 'lion' (lion can mean a brave person).
'full of' is an insertion indicator.
'appeal' becomes 'it' ('it' can mean something attractive or appealing).
'lion' going around 'it' is 'lition'.
'demo'+'lition'='DEMOLITION'
(Other definitions for demolition that I've seen before include "ruin" , "explosion" , "Knocking down" , "Licking" , "defeat" .)