Party inflicting damage around River Wye, initially (5-7)
I believe the answer is:
house-warming
'party' is the definition.
(I've seen this before)
'inflicting damage around river wye initially' is the wordplay.
'inflicting damage' becomes 'harming' (to harm something is to inflict damage on it).
'around' is an insertion indicator.
'river' becomes 'ouse' (Yorkshire river).
'initially' says to take the initial letters.
The first letter of 'wye' is 'w'.
'ouse'+'w'='ousew'
'harming' going around 'ousew' is 'HOUSE-WARMING'.
(Another definition for house-warming that I've seen is " Celebration of moving".)