Wild sheep sound out of breath (7)
I believe the answer is:
rampant
'wild' is the definition.
(I've seen this before)
'sheep sound out of breath' is the wordplay.
'sheep' becomes 'ram' (ram is a kind of sheep).
'sound out of breath' becomes 'pant' (I've seen this before).
'ram'+'pant'='RAMPANT'
(Other definitions for rampant that I've seen before include "Showing unrestrained growth" , "Rife" , "Unrestrained and violent" , "Unchecked (and violent?)" , "Unrestrained, flourishing excessively" .)