Annoyed editor changed sides (7)
I believe the answer is:
crossed
'changed sides' is the definition.
The answer and definition can be both to do with motion as well as being past participle verbs.
Maybe there's a link between them I don't understand?
'annoyed editor' is the wordplay.
'annoyed' becomes 'cross' (cross can mean angry).
'editor' becomes 'ed' (abbreviation).
'cross'+'ed'='CROSSED'
Can you help me to learn more?
(Other definitions for crossed that I've seen before include "Went over to the other side" , "Traversed" , "Came over and < annoyed" , "Passed" , "Intersected; opposed" .)