What does the cryptic crossword clue "Athlete coming from rear in preliminaries (5)" mean?

The definition is "Athlete". The wordplay uses a hidden word. RELIM (reversal="RELIM") = MILER; definition: "Athlete" The answer is MILER.

Athlete coming from rear in preliminaries (5)

Guardian Cryptic #29645 | 22 Down | 2025-03-18 flower