Temper displayed by athlete finally breaking record (6)
I believe the answer is:
anneal
'temper' is the definition.
(I know that temper can be written as anneal)
'athlete finally breaking record' is the wordplay.
'athlete finally' becomes 'e' (I am not sure about this - if you are sure you should believe this answer much more).
'breaking' means one lot of letters goes inside another.
'record' becomes 'annal' (I've seen this before).
'e' placed inside 'annal' is 'ANNEAL'.
'displayed by' acts as a link.
Can you help me to learn more?
(Other definitions for anneal that I've seen before include "Toughen by a process of gradually heating and cooling" , "Temper, harden" , "Toughen using heat" , "Heat and cool to temper or toughen" , "Harden by heating and cooling" .)