Barely runs on narrow lines (7)
I believe the answer is:
streaks
'barely runs' is the definition.
'streaks' can be an answer for 'runs' (streaking is a kind of running). I am not certain of the 'barely' bit.
'on narrow lines' is the wordplay.
I cannot quite understand how this works, but
'on' could be 're' ('on' can be mean 'with reference to') and 're' is located in 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.)" .)