Defensive unit errors somewhat upset followers (7)
I believe the answer is:
retinue
'followers' is the definition.
(retinue can mean an important person's followers)
'defensive unit errors somewhat upset' is the wordplay.
'somewhat' indicates the answer is hidden within the clue.
'upset' says the letters should be written in reverse.
'euniter' can be found hidden inside 'defensive unit errors'.
'euniter' in reverse letter order is 'RETINUE'.
(Other definitions for retinue that I've seen before include "Entourage, followers" , "Group of attendants for VIP" , "Group of assistants" , "Body of followers" , "Train; attendants" .)