Hoodlum

[hood-luh m, hoo d-] /ˈhud ləm, ˈhʊd-/

noun
1.
a thug or gangster.
2.
a young street ruffian, especially one belonging to a gang.
/ˈhuːdləm/
noun
1.
a petty gangster or ruffian
2.
a lawless youth
n.

popularized 1871, American English, (identified throughout the 1870s as “a California word”) “young street rowdy, loafer,” especially one involved in violence against Chinese immigrants, “young criminal, gangster;” it appears to have been in use locally from a slightly earlier date and may have begun as a specific name of a gang:

The police have recently been investigating the proceedings of a gang of thieving boys who denominate themselves and are known to the world as the Hoodlum Gang. [San Francisco “Golden Era” newspaper, Feb. 16, 1868, p.4]

Of unknown origin, though newspapers of the day printed myriad fanciful stories concocted to account for it. A guess perhaps better than average is that it is from German dialectal (Bavarian) Huddellump “ragamuffin” [Barnhart].

What the derivation of the word “hoodlum” is we could never satisfactorily ascertain, though several derivations have been proposed; and it would appear that the word has not been very many years in use. But, however obscure the word may be, there is nothing mysterious about the thing; …. [Walter M. Fisher, “The Californians,” London, 1876]

noun

A petty criminal; a street tough

[1868+; origin unknown, although many suggestions have been made; the term appears to have originated in San Francisco]