Well, I translated something here, with help of Google language tools. With some changes of mine.   Of course, it can improved. 

   Ah, not a translation; I would say a version (to spice it up a bit! hehe).

   Ah, again.   Don´t ever ask me why zebra didn´t get there, I have some theoretical opinions: maybe because she doesn´t belong to the Brazilian fauna or maybe there wasn´t no zebra at the time in Rio´s zoo...

  In fact ''dar zebra'' may have two slightly different senses:
  To be/have a surprise result in sports, or to happen a reversal (in somebody´s fate, inclusive in sports), the end result is that one way or the other you have an unantecipated result/outcome (not necessarily a bad one, only that you didn´t expected it happen)

   Still, "dar zebra":
"to have an unexpected result/to happen an unexpected outcome"
"the underdog (team) wins/won, that is, in a competition (politics, sports and creative works) the group popularly expected to lose indeed won!

   Look upWiki: underdog

   Plus, "dar zebra" means "when something/everything screw up" (or did not go well, for you, for your team etc).

    In the positive sense, when you have "the improblabe, the surprising, the unexpected and amazing" (sometimes for better, other times for worse-context wise) all in one piece, you have "uma zebra"

http://noticias.terra.com.br/educacao/vocesabia/interna/0,,OI3045174-EI8402,00.html

   Imagine você ter jogado na loteria e ficar sabendo que os números divulgados do vencedor são os mesmos que o do seu bilhete. Porém, quase em êxtase, ao procurá-lo no bolso, o bendito papel já não está mais lá. É, pode considerar que "deu zebra".
   A origem da expressão "dar zebra", utilizada nas situações em que o resultado foi algo impossível de acontecer, surgiu no popular Jogo do Bicho, como informa o professor de Língua Portuguesa Ari Riboldi.     Segundo conta em seu livro O bode expiatório, a zebra não está entre os 25 animais que emprestam o nome a essa loteria ilegal, por isso, interpreta-se o fato como uma "tragédia" inesperada.
       Ao longo do tempo, como descreve a obra, a expressão passou a ganhar popularidade no futebol antes de se espalhar para as demais modalidades esportivas.        

     Um exemplo disso é quando uma equipe, considerada favorita pela sua maior qualidade, é derrotada por outra que não tinha qualquer chance de vitória.
     Atualmente, o termo ganhou às ruas e é usado no dia-a-dia das pessoas. Portanto, não teste a sua "sorte" para não correr o risco de usar a expressão.
   

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» O que significa "boi de piranha"?
» Qual a origem de "rodar a baiana"?
» O que significa "lavar a égua"?
» Veja mais dúvidas de história

http://noticias.terra.com.br/educacao/vocesabia/interna/0,,OI3045174-EI8402,00.html

   "Deu zebra"? Saiba a origem da popular expressão
   "Deu zebra"? Learn the origin of the expression.

   Imagine you have played the lottery, after the numbers are drawn and announced, you find out you your number selection match all those numbers, you are the winner!
Then  soon after that, you find out that a guy has the very same numbered ticket (the very same number selection!).
    However, almost in ecstasy, as you look for the ticket in your pocket, the blessed ticket is no longer there. You can sure that something bad or very unexpected happened ("deu zebra." - something went wrong.)   What went wrong? What´s happening/ what´s the matter/ what´s going on…oh my god!

    The origin of the expression "dar zebra", used in situations where the result was something impossible to happen (or had to be, in the above case), appeared in the popular Brazilian number racket, acording to the professor of Portuguese Ari Riboldi.      

    By his account in his book The Scapegoat, zebra is not among the 25 animals that lend their name to such illegal lottery, so it is interpreted this as a  unexpected "tragedy".

    Over time, as he describes the in the work, the term started to gain popularity in soccer before spreading to other sports.               An example of that, is when a team considered a favorite for its higher quality, is defeated by someone who had no chance of victory.
     Nowadays, the term went to the streets and is used in day-to-day talking. So, don´t push your luck/don´t stretch your luck/don´t expect too much of luck.
     If you do, chances are you are going to use the expression.

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