What does the cryptic crossword clue "Unofficially, hen do site gets in a mess (2,3,4)" mean?

The wordplay uses an anagram. anagram of HEN + DO + SITE = ONTHESIDE The answer is ONTHESIDE.

Unofficially, hen do site gets in a mess (2,3,4)

Guardian Cryptic #29581 | 30 Across | 2025-01-02 flower