Spectators' disapproval taps into poor performance by runner (4,8)
I believe the answer is:
slow handclap
'spectators' disapproval' is the definition.
The definition suggests a singular noun which matches the answer.
'taps into poor performance by runner' is the wordplay.
I cannot really see how this works, but
'taps' could be 'handc' (hot and cold) and 'handc' is located in the answer.
'poor' could be 'low' (similar in meaning) and 'low' is found in the answer.
The remaining letters 'slap' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for slow handclap that I've seen before include "Audience's sign of displeasure" , "audible rebuke" , "Ironic or disapproving applause" , "Expression of disapproval" , "indication of disapproval" .)