Best get rid of ground-breaking tool (7)
I believe the answer is:
pickaxe
'ground-breaking tool' is the definition.
(I've seen this before)
'best get rid of' is the wordplay.
'best' becomes 'pick' (I've seen this before).
'get rid of' becomes 'axe' (I've seen this before).
'pick'+'axe'='PICKAXE'
(Other definitions for pickaxe that I've seen before include "it's needed to break new ground" , "Mattock" , "Tool to break rocks" , "strike-breaker?" , "Wooden-handled iron tool with a curved head, pointed at both ends" .)