Nearly avoid oddly crude error at the Crucible (6)
I believe the answer is:
miscue
'error at the crucible' is the definition.
(error in snooker - the Crucible is a snooker venue)
'nearly avoid oddly crude' is the wordplay.
'nearly' means to remove the last letter.
'avoid' becomes 'miss' (miss can mean to avoid).
'oddly' indicates alternate letters (letters in the odd-numbered positions are used).
The alternate letters of 'crude' are 'cue'.
'miss' with its last letter taken off is 'mis'.
'mis'+'cue'='MISCUE'
(Other definitions for miscue that I've seen before include "Bad stroke in snooker" , "Hit snooker ball badly" , "Faulty snooker shot" , "Parapraxis (from a term used in billiards)" , "Bad hit in snooker" .)