Barely runs on narrow lines (7)
I believe the answer is:
streaks
'barely runs' is the definition.
(to streak is to run while naked or bare)
'on narrow lines' is the wordplay.
I cannot really understand how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is found within the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for streaks that I've seen before include "Runs naughtily nude in public" , "Stripes for skaters" , "Skaters (anag.)" .)