Almost stop hero becoming a stud (8)
I believe the answer is:
stallion
'a stud' is the definition.
(I've seen this before)
'almost stop hero' is the wordplay.
I cannot really understand how this works, but
'stop' could be 'stall' (stalling is a kind of stopping) and 'stall' is found within the answer.
The remaining letters 'ion' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
'becoming' acts as a link.
Can you help me to learn more?
(Other definitions for stallion that I've seen before include "Male horse, often used for breeding" , "Male horse kept for breeding" , "Male steed" , "Male horse lost in atolls" , "Mount" .)