Poke right inside seedcase (4)
I believe the answer is:
prod
'poke' is the definition.
('prod' can be a synonym of 'poke')
'right inside seedcase' is the wordplay.
'right' becomes 'r' (common abbreviation).
'inside' means one lot of letters goes inside another.
'seedcase' becomes 'pod' ('pod' can be a synonym of 'seedcase').
'r' inserted into 'pod' is 'PROD'.
(Other definitions for prod that I've seen before include "Poke (with a finger, etc)" , "Drop (anag.)" , "Poke, jab, nudge" , "Goad, stimulate into action" , "Motivate; jab" .)