Grass-cutter can become chesty (6)
I believe the answer is:
scythe
'grass-cutter' is the definition.
(I've seen this before)
'become chesty' is the wordplay.
'become' is an anagram indicator.
'chesty' is an anagram of 'SCYTHE'.
'can' is the link.
(Other definitions for scythe that I've seen before include "One cuts" , "farm hands once had to work with" , "cut down the weed?" , "Old hay cutter with long handle and curved blande" , "Old hands-wielded grass or crop cutter" .)