I am in the game period where I get one for almost every captain-lead battle. I have not re-tested it but I would propose an explanation: to get a Man of the Hour, the captain unit (the one with the yellow star) has to fight bravely. Maybe be the unit that causes the more ennemy casualties, or have more than n deads, etc. I believe it is something like that because the last time I did not get MotH, it was because the captain unit had not fought at all.

Any thoughts?