Starts to delve into ground, doing this (3)
I believe the answer is:
dig
'doing this' is the definition.
The definition suggests a singular noun which matches the answer.
'starts to delve into ground' is the wordplay.
'starts to' suggests taking the first letters.
The first letters of 'delve into ground' is 'DIG'.
(Other definitions for dig that I've seen before include "Understand" , "criticism" , "Sly remark; excavate" , "Appreciate - archaeological research" , "critical remark" .)