In barn record calamity on field for farm worker (8)
I believe the answer is:
sheepdog
'farm worker' is the definition.
'in barn record calamity on field' is the wordplay.
'in' indicates putting letters inside.
'barn' becomes 'shed' (I've seen this before).
'record' becomes 'ep'.
'calamity on field' becomes 'og' (own goal in football).
'shed' going around 'ep' is 'sheepd'.
'sheepd'+'og'='SHEEPDOG'
'for' is the link.
(Other definitions for sheepdog that I've seen before include "Shaggy-haired canine" , "One drives over fields" , "Working farm animal" , "Pastoral assistant?" , "Collie, perhaps" .)