Dash for one, scrambling up mountain track (11,4)
I believe the answer is:
punctuation mark
'dash for one' is the definition.
(dash is a kind of punctuation mark)
'scrambling up mountain track' is the wordplay.
'scrambling' indicates anagramming the letters.
'up'+'mountain'+'track'='upmountaintrack'
'upmountaintrack' anagrammed gives 'PUNCTUATION MARK'.
(Other definitions for punctuation mark that I've seen before include "Possibly stop" , "period in New York, perhaps? - with 5d" , "period in US, say" .)