So, you've grabbed the opponent by the sleeve, snatched him off balance as you pulled yourself to a safer location outside his arms, and trapped his arm against your hip. Now comes probably the most versatile motion in the whole kata - The down block.
Screeeeeech! Wait, what? The down block that you learn on day#1 of practice is the most versatile thing in naihanchi!?!?
Yep - This isn't your grand-dad's down block. It's good for a lot more than knocking a front kick aside. The motion that we call downblock is really a general-purpose smashing, brushing, defending-while-attacking, grabbing-and-pulling, offbalance and pinning thing..
It is so versatile that Rick Clark has written a book called 75 Down Blocks! Looks interesting, though I haven't gotten a chance to read it.
Coming after the teacup in naihanchi, the downblock is typically assumed to be an elbow smash to the trapped arm or else a crushing blow to the neck of the off-balanced opponent. But there is really no end to the application for it. When combined with some of the naihanchi footwork, the downblock even becomes a kosotogari (one of the first sweeps we teach in judo).
Hint: We just call it "down block" to have a simple name to call it. You could call it "Fred's multipurpose arm motion #1" if you wanted to, but "down block" seems more... I don't know... evocative?