Tap observed to be crooked (8)
I believe the answer is:
cockeyed
'be crooked' is the definition.
('cockeyed' can be similar in meaning to 'crooked')
'tap observed' is the wordplay.
'tap' becomes 'cock' (I've seen this before).
'observed' becomes 'eyed' (I've seen this before).
'cock'+'eyed'='COCKEYED'
'to' is the link.
(Other definitions for cockeyed that I've seen before include "Senseless" , "at an angle" , "cuckoo" , "Crooked or askew, looking like rooster?" , "Skew-whiff" .)