Chacas is a slang term, often used in Mexico, to refer to 'gang members' or 'tough guys'. It's a word that gives insight into a specific cultural context and isn't commonly found in everyday Spanish lessons.
In the song, the protagonist, now a successful lawyer, mentions "Ayudando chacas que en duros aprietos se han mirado" (Helping tough guys who have found themselves in difficult situations). This highlights his background and the community he serves, making chacas a key word for understanding the song's narrative and setting.
Legado 7 built this corrido around a real person: Alejo Lugo, who grew up close to "la maña" (organized crime, the street code plenty of corridos glorify) alongside a friend who chose books instead. "Uno estudioso y el otro puro desmadre tiraba" (one was studious, the other pure chaos) sets up the twist, because it's Lugo, not the studious friend, who ends up "Ahora en Riverside, soy un abogado" (now in Riverside, I'm a lawyer). The song frames crossing into the US as the hinge point: "Un día brincamos pa'l otro lado" (one day we jumped to the other side), after which he throws himself into school, saying flatly "Me apliqué en la escuela, siempre pinté pa' ser abogado" (I applied myself in school, I always aimed to be a lawyer).
His grandfather Nino gets the warmest lines in the song, repeated once mid-song and again right at the end: "Y a su papá Nino, siempre lo recordaremos, porque sus consejos al viejo lograron" (we'll always remember his father Nino, because the old man's advice paid off). Everything after that plays like a victory lap. Lugo now spends his days "Ayudando chacas que en duros aprietos se han mirado" (helping girls who've found themselves in tough jams), the band sends a shoutout to his friend "el R1," and the hook "Puro Legado 7" ties the band's own name to somebody else's success story, which is corrido tradition in a single line.