[RobW]

There are two aspects to your very reasonable question.

One is about adjDX. Can a low DX fighter defend against a high DX one? The answer to this is yes. Assuming they've met the movement requirements, a low DX figure can change their option to include Defending, e.g. from option (j) Shift and Attack, to option (k) Shift and Defend.

The second aspect to this question is that it sounds like Player 1 starts the turn disengaged and moves 1/2 their MA. The RAW seem to be very clear that unless you are engaged at the time of your figure's movement, you can't choose the Defend option. That is, there is no option for disengaged figures, move and defend.

There has been no official clarification on this, but many people here (including me) think this can only be a mistake in the rules.

Why a mistake? Well for one thing, a figure can't normally defend against a jab, as it will not have been engaged at the time of its movement.