WordNet (r) 3.0 (2006):

palooka
    n 1: a second-rate prize fighter [syn: stumblebum, palooka]

Moby Thesaurus II by Grady Ward, 1.0:

31 Moby Thesaurus words for "palooka":
   Chinese boxer, bantamweight, black belt, boxer, brown belt,
   bruiser, featherweight, fighter, fisticuffer, flyweight, gawk,
   heavyweight, karate expert, klutz, light heavyweight, lightweight,
   lobster, looby, lout, lubber, lug, lummox, lump, middleweight, oaf,
   prizefighter, pug, pugilist, savate expert, sparrer,
   welterweight