I played a siege defence last night where the castle is surrounded by a river with two bridges crossing to the central island, where the castle is built. I thought this would be a cake walk but was concerned not to over-commit in deployment so had most forces in the castle but 3 Ashigaru archers behind a single Yari Ashigaru unit at my end of each bridge.

The gong struck, it turned out the enemy had set up opposite only one bridge so I pulled the force from other back behind the walls and waited as the enemy advanced.

I must have gone back to checking on who i had manning which section of wall for a second because the next minute I looked back, the attackers were wading through the river and I realised my 4 units of Ashigaru were caught out in the open!

I had to sacrifice my Yari unit but i managed to get the 3 Yumi units back inside safe enough.

Not exactly the AI doing me over there, but I hope that serves as a warning for others! This was a castle to the south west of Kyoto by the way.