Red herring is an argument, given in reply, that does not address the original issue. Critically, a red herring is a deliberate attempt to change the subject or divert the argument.
This isn't so much a fallacy as it is an evasion tactic. The red herring is similar to a "wild goose chase." When someone leads the debate off on a red herring, they are trying to divert attention away from a particular argument, and toward some inconsequential statement that you may have made, or inventing some tangent to go off on. Creationists often use this when they attack the Big Bang Theory to try and prove evolution wrong. The Big Bang and evolution are completely separate theories, and are not mutually inclusive. The Creationist trying to debate the Big Bang is a red herring.
"Evolution is impossible because the Big Bang is a totally unacceptable theory because it defies the word of our loving Creator, He who sent His only Son, our Lord to...[continue with mindless religious yammering ad infinitum]."
The Big Bang has nothing to do with evolution. If it was proven wrong tomorrow, it wouldn't change the fact that organisms evolve to adapt to their environment, or they die.