If you look at about the 7:40 mark on the video you will hear Lennox make a statement that goes something like this: Since you are an Atheist and you don't think there is any rationality behind the existence of the universe, you therefore believe it was a freak accident.

According to my Fundamentals of Critical Argumentation book, this is an argument from commitment. Basically what Lennox is doing is drawing a plausible conclusion that since Dawkins is an atheist, and an atheist doesn't believe in a creator of the universe to provide order, he therefore believes it was a freak accident, which is the opposite of order. This might hold up if those are the only two choices--either a universe with order and a creator, or a universe without it and chaos. However, as Dawkins goes on to state, there is a third option, and that is a model based on Darwin's natural selection theory.

So this argument becomes a fallacy because it does not follow that simply being an atheist demands that we believe that the universe was a freak accident. There are two critical questions that Lennox should have asked before making this argument. 1) What evidence is there to support the claim that Dawkins is an atheist that is committed to this "freak accident" theory and is there any evidence to suggest that he might not be? 2) Is there room for questioning whether this is an exception to the case or a general rule?

I think to most Christians it would seem that not supporting a universe with a creator might make it seem like atheists support a universe that was a freak accident, but that just isn't true. Here's where educating yourself on what an atheist really holds to be the truth would be very beneficial to a Christian before starting with this weak argument.