I recall "re-sort" and "again" being used by RT in the past, so probably the same compiler.
(Chambers 12th does not show "again" in their list of anagram indicators)
Strange that you should find it hard. I found it the easiest for several weeks!
I've been looking for this answer to "horse" (10ac) whenever a horse clue has come up! It is so obvious but I do not remember it before.