Actually, for apparently different reasons, I'm singing a similar tune to Dane in this case. Hall knew something was wrong after the half. If he doesn't think he can overcome it, what will come of running a 2:15-2:20 marathon? What risk is he undertaking, possibly even an unknown risk? For his health and competitive future, this may be the right decision for him to make. It will allow him to figure out what's wrong and come back more quickly than had he torn his body apart running a marathon his body wasn't ready for.
Perhaps my writing in the above quoted text was lacking in its true intentions but you definitely are saying the exact same thing as I was intending to.