One of the first to take a knock (6)
I believe the answer is:
opener
'a knock' is the definition.
The answer and definition can be both related to natural events as well as being singular nouns.
Maybe there's an association between them I don't understand?
'one of the first to take' is the wordplay.
'one of' becomes 'o'.
'the first to' becomes 'pene' (I can't justify this - if you can you should give a lot more credence to this answer).
'take' becomes 'r' (abbreviation for 'recipe', Latin for 'take').
'o'+'pene'+'r'='OPENER'
Can you help me to learn more?
(Other definitions for opener that I've seen before include "Tool for taking lid off a can" , "First goal in game" , "First in batting order" , "Kitchen item" , "First act" .)