If we're going to be factually accurate, he was below .400 (.39955) heading into the last day, but they had a double-header that day and he still played both games despite being over .400 after getting 4 hits in the first one, when an 0-5 (but not an 0-4) in the second one would have dropped him under. See a summary here: http://sabr.org/research/day-ted-williams-became-last-400-hitter-baseball
Ok. But I think he was confident after that first game that there was nearly no chance he could blow it in the second game.
