Jumper cleared ditch in Irish festival (6)
I believe the answer is:
fleadh
'irish festival' is the definition.
(I've seen this before)
'jumper cleared ditch' is the wordplay.
'jumper' becomes 'flea' (something that jumps).
'cleared' suggests removing the centre (the inside letters are cleared out).
'ditch' with its middle removed is 'dh'.
'flea'+'dh'='FLEADH'
'in' acts as a link.
(Other definitions for fleadh that I've seen before include "festival in Cork?" , "Irish festival" .)