Notice jumpers are going up (4)
I believe the answer is:
spot
'notice' is the definition.
(thesaurus)
'jumpers are going up' is the wordplay.
'jumpers' becomes 'tops'.
'are going up' says the letters should be written in reverse.
'tops' back-to-front is 'SPOT'.
(Other definitions for spot that I've seen before include "Drop of rain" , "Small mark or stain" , "Notice - place" , "Difficult situation" , "Small round mark" .)