Runner perhaps turned up at LSE (5)
I believe the answer is:
pulse
'runner' is the definition.
Although both the answer and definition are singular nouns, I cannot understand how one could define the other.
'turned up at lse' is the wordplay.
'turned' says the letters should be written backwards.
'at' is a charade indicator (letters next to each other).
'up' reversed gives 'pu'.
'pu'+'lse'='PULSE'
'perhaps' is the link.
Can you help me to learn more?
(Other definitions for pulse that I've seen before include "It beats - peas and beans" , "Series of rhythmic beats" , "A vital sign turning" , "Beat - legumes" , "Heartbeat; legume" .)