What does the cryptic crossword clue "Colt’s foal? Bad lot (3,2,1,3)" mean?

The definition is "Colt’s foal? Bad lot". The wordplay uses a cryptic definition. Cryptic definition The answer is SONOFAGUN.

Colt’s foal? Bad lot (3,2,1,3)

Guardian Cryptic #29683 | 24 Across | 2025-05-01 flower