Meet round side and do a runner (4)
I believe the answer is:
flit
'do a runner' is the definition.
(I've seen this before)
'meet round side' is the wordplay.
'meet' becomes 'fit' (fitting is a kind of meeting).
'round' indicates putting letters inside.
'side' becomes 'l' (abbreviation for left).
'fit' going around 'l' is 'FLIT'.
'and' acts as a link.
(Other definitions for flit that I've seen before include "Flutter - leave by moonlight?" , "Scurry lightly" , "Decamp (by moonlight?)" , "Run away (by moonlight?)" , "it may be done by moonlight" .)