Self-confidence therefore runs out (3)
I believe the answer is:
ego
'self-confidence' is the definition.
(I've seen this before)
'therefore runs out' is the wordplay.
'therefore' becomes 'ergo' (I've seen this in another clue).
'runs' becomes 'r' (cricket abbreviation).
'out' is a deletion indicator.
'ergo' with 'r' taken away is 'EGO'.
(Other definitions for ego that I've seen before include "Self-esteem, conceit" , "Conceit - the Latin "I"" , "Conscious mind" , "Person's sense of self" , "Personal pride" .)