To add more information to @walen's answer, I'd like to add that the RAE's Spanish Grammar contains a whole chapter about the -azo suffix (link in Spanish). It basically says that the -azo suffix comes from latin -acĕus and it forms a number of compounds in Spanish that refer to hits and sudden actions. So cabezazo means a hit with (or in) the head. The base word is usually a noun but it can also be a verb, as in frenazo (a sudden braking).
The producivity of this suffix is outstanding, as you can form compounds with almost every noun: zapatazo would mean a hit with a shoe, and not a big shoe. So the Gramática warns us that due to the big amount of possible compounds it is not possible to register them all in the dictionary.
The compound forms that refer to hits come mainly from weapons, instruments, utensils and physical objects in general: banderillazo, barquinazo, bastonazo, batazo, botellazo, cabezazo, cachiporrazo, cantazo, cuentazo, culatazo, escobazo, fierrazo, filazo, garrotazo, ladrillazo, macanazo, machetazo, martillazo, palazo, palmetazo, pepazo, piquetazo, puyazo, quiñazo, rolazo, sartenazo, talegazo, tetuntazo, toletazo, trancazo, varetazo and many more. You can also use parts of the body: codazo, puñetazo, rodillazo, testarazo, zarpazo, derechazo, zurdazo.
Please check the link above to get more information about the subject (quite interesting even for Spanish-language natives).