Biscuit gets cracking after one in seedy bar (9)
I believe the answer is:
digestive
'biscuit' is the definition.
(I've seen this before)
'gets cracking after one in seedy bar' is the wordplay.
'cracking' indicates an anagram.
'after' says to put letters next to each other.
'one' becomes 'I' (Roman numeral).
'in' indicates putting letters inside.
'seedy bar' becomes 'dive' (as in a dive bar).
'gets' anagrammed gives 'gest'.
'gest'+'i'='gesti'
'gesti' going inside 'dive' is 'DIGESTIVE'.
(Another definition for digestive that I've seen is " Type of biscuit".)