Track circuits (4)
I believe the answer is:
laps
'track circuits' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for laps that I've seen before include "Circuits of track" , "Scoops up with the tongue" , "Drinks; circuits" , "Pals doing rounds of the track" , "Circuits of a racetrack" .)