What does the cryptic crossword clue "Huge wave? It comes up catching U.S. man when swimming (7)" mean?

The definition is "Huge wave?". The wordplay uses an anagram. anagram of IT + U.S. + MAN = TSUNAMI; definition: "Huge wave?" The answer is TSUNAMI.

Huge wave? It comes up catching U.S. man when swimming (7)

Daily Mail Cryptic #17110 | 21 Down | 2023-06-01 flower