Dog starting to retrieve cricket balls (5)
I believe the answer is:
rover
'dog' is the definition.
(I've seen this before)
'starting to retrieve cricket balls' is the wordplay.
'starting to' indicates taking the first letters.
'cricket balls' becomes 'over' (type of cricket delivery).
The initial letter of 'retrieve' is 'r'.
'r'+'over'='ROVER'
(Other definitions for rover that I've seen before include "gypsy" , "Pirate; dog's name" , "One who wanders about" , "Person who wanders - a good name for dog" , "A vagrant" .)