What does the cryptic crossword clue "This ahead for person taking over? Unlikely (6,3)" mean?

The definition is "This ahead for person taking over? Unlikely". The wordplay uses a cryptic definition. Cryptic definition The answer is BOWLERHAT.

This ahead for person taking over? Unlikely (6,3)

Guardian Cryptic #29375 | 22 Across | 2024-05-06 flower