Rests, and turns back for the bridge (4)
I believe the answer is:
naps
'rests' is the definition.
(I've seen this in another clue)
'back for the bridge' is the wordplay.
'back for' is a reversal indicator (I've seen 'backing for' mean this).
'the bridge' becomes 'span' ('span' can be a synonym of 'bridge').
'span' in reverse letter order is 'NAPS'.
'and turns' acts as a link.
I am not very happy about this link. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for naps that I've seen before include "Span including short sleeps" , "Snoozes" , "Tips; sleeps" , "Takes forty winks" .)