Being agitated may be a source of quarrels (7)
I believe the answer is:
aquiver
'being agitated' is the definition.
'a source of quarrels' is the wordplay.
'source of quarrels' becomes 'quiver' (a quiver contains arrows - a quarrel is an arrow).
'a'+'quiver'='AQUIVER'
'may be' is the link.
(Other definitions for aquiver that I've seen before include "Trembling" , "far from steady" , "shaking" , "Flickering" , "shuddering" .)