What does the cryptic crossword clue "Don overturned tennis umpire's call (3,2)" mean?

The definition is "Don". The wordplay uses a reversal. reverse of PUTON = NOTUP; definition: "tennis umpire's call" The answer is NOTUP.

Don overturned tennis umpire's call (3,2)

Guardian Cryptic #28953 | 6 Down | 2022-12-29 flower