What does the cryptic crossword clue "Cast is turning fat – a hindrance when on the road (7)" mean?

The wordplay uses a reversal. LOB (reversal="throw, cast") + LARD (synonym="fat") = BOLLARD The answer is BOLLARD.

Cast is turning fat – a hindrance when on the road (7)

Guardian Cryptic #29226 | 24 Across | 2023-11-13 flower