Nerves, distraction, possibly even illness or exhaustion. I only throw it out there as a possibility, not that it’s particularly likely.
That said, a “star” level player should be able to handle such things (minus illness, perhaps) and not let it affect their “game”. I mean, if scrutiny and pressure are going to depress your abilities, that does’t bode well for big-game performance, now, does it?
Certainly illness could case such a performance but I heard nothing of him being sick. As somebody who has been working out regularly and intensely for a long time I'll tell you that one has an automatic tendency to focus when you're holding two hundred pounds over your head. Nerves and distractions pretty much disappear.