Some reckless pedestrians belted along (4)
I believe the answer is:
sped
'belted along' is the definition.
('speed' can be a synonym of 'belt along')
'some reckless pedestrians' is the wordplay.
'some' says the answer is hidden in the clue (some of the parts of the word are used).
'SPED' can be found hidden inside 'reckless pedestrians'.
(Other definitions for sped that I've seen before include "Rushed" , "Raced, hurried" , "Travelled quickly" , "Hastened" , "was 8 [FLEET]" .)