It reads:

R Commit: After your opponent plays an attack (not as a block), they commit X cards in their staging area. X equals the difference between the number of cards in your hand and the number of cards in your opponent's hand.

Now if my opponent would have to commit more cards than are available,

I.E, he must commit 5 cards but only has 4 ready. would he fulfill as much as possible, commiting his whole board and ignoring the 5th card,

Or is it something akin to Genocide's shennanigans and if he can't commit the exact number he commits none?

This is purely a wording question.

They would have to commit as many cards in their staging area as they possibly can......if they have to commit 5 and only have 4 to commit then they commit 4 unless otherwise stated on the R.

Wurm-Z said:

Correct.