Heading off, hobbled with little energy — cramp? (6)
I believe the answer is:
impede
'cramp?' is the definition.
(thesaurus)
'heading off hobbled with little energy' is the wordplay.
'heading off' means to remove the first letter.
'hobbled' becomes 'limped' ('limp' can be a synonym of 'hobble').
'with' is a charade indicator (letters next to each other).
'little' suggests taking the first letters.
The initial letter of 'energy' is 'e'.
'limped' with its first letter taken off is 'imped'.
'imped'+'e'='IMPEDE'
(Other definitions for impede that I've seen before include "Delay progress of (something)" , "Hinder or hold up" , "Delay, be an obstacle" , "Bar" , "Hinder, be obstructive" .)