They cut some of the grass (6)
I believe the answer is:
blades
I believe this clue is a double definition.
'they cut' is the first definition.
(I've seen this before)
'some of the grass' is the second definition.
(I've seen this before)
(Other definitions for blades that I've seen before include "They cut" , "cutters" , "Knife edges or dashing fellows" , "Football club nickname" , "Leaves of grass or cutting tools" .)