Stop me backing on to street (4)
I believe the answer is:
stem
'stop' is the definition.
(stemming is a kind of stopping)
'me backing on to street' is the wordplay.
'backing' says the letters should be written in reverse.
'on' says to put letters next to each other.
'to street' becomes 'st'.
'me' written backwards gives 'em'.
'em' put after 'st' is 'STEM'.
(Other definitions for stem that I've seen before include "Check - part of a plant" , "Ski turn and plant stalk" , "Supporting structure" , "Vertical part of flower or drinking glass" , "part of pipe" .)