The Defend option in tactical battles plays a one second animation. It switches the mouse cursor to the spell wand, showing a 6x6 grid that looks like a casting radius. This goes on for about 12 seconds and then plays the final animation, a shield above the units head. When the unit moves, the shield stays on that square. 

It is enough t o prevent me from ever using the defend option. I noticed that the AI does not have the same issue with defend, at least for shield town guards. 

Ogres seem to have a ranged spell called Stabbing or something that has a 6 second delay in the animation. I have killed all the ogres so I will have to post on that one later.