What does the cryptic crossword clue "Upset Sid and Burt when swimming (7)" mean?

The definition is "Upset". The wordplay uses an anagram. anagram of SID + BURT = DISTURB; definition: "Upset" The answer is DISTURB.

Upset Sid and Burt when swimming (7)

Daily Mail Cryptic #17102 | 9 Across | 2023-05-22 flower