rap‧scal‧lion, n. /ɹæpˈskæljən/
Literally, “a criminal who is not yet mature.” “Rap” is a colloquialism for being accused or convicted of a crime. (See “a bad rap.”) Scallions were and still are thought to be an immature variety of onion or leek. Together, the term is often applied to child troublemakers.
Entirely unrelated to MC Rap Scallion, who adopted the word for the suitability of its initial syllable to his profession.