One (brutal) way is to enter off the line of attack, push down on Uke‘s striking arm, then extend your outside arm right away with an open palm into Uke‘s face to shock him back and down. If it is insisted the arm be locked and the palm target right through Uke‘s face, I would practice this as slowly as possible until time runs out.

Another (kind) way is with blending.

As the tsuki comes in, do an irimi parry with your front tegatana (but don’t chop or do some ridiculous hard block). Tenkan as if you intend to mirror the stance of Uke. With your inside tegatana, rest it on Uke‘s elbow crease so you can feel his arm should he decide to raise it. Kaitensoku (pivot toward Uke). Stay right against Uke. Your outside arm glides over Uke‘s tsuki arm and heads for Uke‘s neck. You then want to ready yourself for a recognizable iriminage throw.

Why do I like this better? It is kinder on Uke; he doesn’t need to be prepared (otherwise injured). It incorporates tenkan, blending and peaceful resolution to the situation. I would rather be friends with a Tori that blends with me to throw me than one palm-fists me in the face unexpectedly.