Biblical inerrancy or that the Bible really accurately describes what happened. The atheist is going to bring it up. I understand why Craig does not go there in a deep way in that he can show that Christianity is reasonable apart from the Bible. Although I think it is effective in his hands, i think not bringing the Bible to bear is not giving the whole message. Of course he isn't trying to give the whole message, just nudge people towards God. I wonder if he thinks the Bible does have contradictions and conflicts. I'll be looking into that soon. William Lane Craig is a philosopher and historian not a theologian. Therefore I want to be careful not to read things into what he believes that is not there. Follow the link below to listen to the debate yourself.
Apologetics 315: William Lane Craig vs. Massimo Pigliucci Debate MP3