I was playing Oda in the 1580 campaign and Imagawa attacked Owari. No problem, set up defense and waited. Imagawa placed archers on each flank and lined up a melee unit assault column ending at the village area _between_ the bridges on the attacker side.

My shiny new muskets got to shoot the crap out of two of his archers, but otherwise, nothing happened. Time expired and I won. Well, I ran the daiymo over the bridge and took a few heads off one of his other archer units, this provoked movement from his assault column.

I then created a custom battle in Owari with AI attacker. Same thing. I ran a kensai across the right bridge (from defender POV) and provoked 1! YS to march out of the column and come to the bridge where it died under the spears of a YA after being shot up a bit. Rinse, repeat. Same thing, one YS came out, and when it got close to the bridge, tried to cross. The rest of the army just sat there.