If a unit of Spearmen is down to its last three trays and has a Front Line Rune Golem in the center tray, normally that Golem cannot be assigned damage because it would violate 22.4 ("22.4 Damage cannot be assigned to any figures in a tray that, if removed from the unit, would cause that unit to be split into two separate groups of trays."). However, if you had two Accuracy icons, you could assign enough damage to that figure to kill it. ("22.5 When performing an attack, the attacker can spend any number of accuracy (?) icons to allow him to assign damage to figure upgrades that cannot normally be assigned damage.").
I'm assuming 22.4 wins, since there are no rules on how to deal with a split unit, and 22.5 is intended to allow damage on figure upgrades when there's still some back ranks in play, but that's not what they actually say.
This could also (maybe?) happen with that one morale card that kills a figure upgrade, though I don't recall the full text.