Leading to extreme upset, declare, having secured runs briskly added to score (10)
I believe the answer is:
allegretto
'score' is the definition.
Both the definition and answer are adjectives. Perhaps there's an association between them I don't understand?
'leading to extreme upset declare having secured runs briskly added' is the wordplay.
I cannot quite understand how this works, but
'to' is present in the answer.
'runs' could be 'r' (cricket abbreviation) and 'r' is found within the answer.
'declare' could be 'allege' (I've seen this before) and 'allege' is located in the remaining letters.
A single letter 't' remains which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
'to' acts as a link.
Can you help me to learn more?
(Other definitions for allegretto that I've seen before include "fairly quickly" , "quite quickly" , "with reasonable rapidity" , "quite fast" , "Moving fairly briskly (music)" .)