Not all cricket enthusiasts observed the last wicket to fall? (5)
I believe the answer is:
tenth
'last wicket to fall?' is the definition.
(tenth wicket in cricket)
'not all cricket enthusiasts observed' is the wordplay.
'not all' indicates a hidden word.
'TENTH' is hidden in the letters of 'cricket enthusiasts observed'.
'the' is the link.
(Other definitions for tenth that I've seen before include "0.1" , "Tithe proportion" , "Fraction in tithe" , "(Decimal?) fraction" , "Decimal part?" .)