User blog comment:SomeoneYouUsedToKnow/SYUTK's V4EFinal - Haven is Doomed - Impressions/Recap/@comment-26397825-20170206153308/@comment-26018514-20170206213820

As someone said, it's that the momentum and angle are off, even if she was on a diagonal course(which seemed not to be the case, it looked like Nora was already falling in her trajectory) the Arm looks like it will hit the hammer's handle just under the head, yet the following scene shows the arm seems to have grabbed the head(ignoring Nora), then acted vastly greater on vertical force which only the hammer(and Nora) had, as opposed to both horizontal(which Nora and the hammer needed to have to intercept the arm in the first place) and along the Z axis the superior force of the arm had.

In other words, the only explanation that makes some sense(in universe) is that the arm twitched upwards reflexively and/or bent irrationally... because otherwise Nora's hammer head should not even have been high enough for Ren to upskirt Nora if her head had replaced it in the wall... and because she dangled from the 4'-5' long handle, the angle is even more impossible.