Arresting type gathering last of bumper yield (4)
I believe the answer is:
crop
'yield' is the definition.
(yield can mean a crop or harvest)
'arresting type gathering last of bumper' is the wordplay.
'arresting type' becomes 'cop'.
'gathering' is an insertion indicator (gather can mean to acquire or bring in).
'last of' says to take the final letters.
The last letter of 'bumper' is 'r'.
'cop' placed around 'r' is 'CROP'.
(Other definitions for crop that I've seen before include "Whip with loop instead of last" , "The handle of a whip, or part of bird's neck" , "where bird food is temporarily stored?" , "farm produce" , "Cut short the season''s yield?" .)