Suggest I stop running (5)
I believe the answer is:
posit
'suggest' is the definition.
(I've seen this in another clue)
'i stop running' is the wordplay.
'running' indicates an anagram (the letters run around to different places).
'i'+'stop'='istop'
'istop' with letters rearranged gives 'POSIT'.
(Other definitions for posit that I've seen before include "Dispose" , "Put forward (argument)" , "advance" , "Put forward (an idea)" , "Put forward as basis for discussion" .)