During our recent dan grading preparation, there's been a lot of questions surrounding muna-dori (lapel grabs). I wanted to share some thoughts on this seldom practiced waza:
First, consider muna-dori waza in the katate-aihanmi family of techniques. In doing so you'll see that the role of uke is to grab with their front hand - which is determined by which foot they are leading with. So, if uke is grabbing with their right hand, it stands to reason that their right foot will be forward for leverage.
Intent of the attack
For this waza uke has two basic intentions. Either they are going to use the muna-dori grip to hold tori in place for a strike or tsuki, or they are going to use the connection to throw nage. The former is probably more likely, similar to kata-dori-men-uchi attacks. However, there are applied techniques that can effectively be used to project and throw tori.
Once tori has responded to the muna-dori grab, their waza is most likely going to involve some form of diagonal projection. Uke should expect tori's weight to be applied their (uke's) front leg, so ukemi is going to involve some sort of turn and mae-ukemi starting with the back (unsecured) leg or foot.
As with most of these type of attacks, tori needs to make a conscious decision at the moment of contact (de-ai) whether or not they are going to let uke really make contact or not. Remember that the actual grab is not the dangerous part (provided you are well grounded in your own center). The "real" attack comes once the connection (musubi) has been made, usually in the form of a strike, thrust or throw. Wait for the initial connection BEFORE you react. Both uke and tori need the connection to exercise their action. Be ready for it and blend accordingly.