Copper runs to get dog (3)
I believe the answer is:
cur
'dog' is the definition.
(cur is a kind of dog)
'copper runs' is the wordplay.
'copper' becomes 'cu' (chemical symbol).
'runs' becomes 'r' (cricket abbreviation).
'cu'+'r'='CUR'
'to get' acts as a link.
(Other definitions for cur that I've seen before include "Mongrel - cowardly person" , "Surly dog (or person)" , "A worthless dog or contemptible person" , "Mangy dog" , "Wretch" .)