Stand outside quarters in a state of the jitters (5)
I believe the answer is:
Here is my best explanation:
'a state of the jitters' is the definition.
I can't judge whether this definition defines the answer.
'stand outside quarters' is the wordplay.
'stand' becomes 'tee' (I've seen this before).
'outside' indicates putting letters inside.
'quarters' becomes 'ns'.
'tee' enclosing 'ns' is 'TENSE'.
'in' is the link.
(Other definitions for tense that I've seen before include "Present, possibly", "Unable to relax", "Attribute of verbs signalling time", "Under emotional strain", "It could be the perfect", "under pressure", "edgy", "in the past, perhaps", "fraught" and "On edge".)