What does the cryptic crossword clue "What sort of jerk would keep lawman on the case? (4)" mean?

The wordplay uses a charade (building blocks). SO (synonym="the case") + DA (synonym="DA") = SODA The answer is SODA.

What sort of jerk would keep lawman on the case? (4)

Times Cryptic #28641 | 21 Across | 2023-06-28 flower