The weather.

[Togakure]

I found that frustrating too, and hence turned off the battle timer. Now, I never play with it on.

When the attackers could swim? I don't remember this being possible with STW, except on a custom map called River Crossing, which didn't have a bridge as I recall, you could just wade through the water at the junction of two rivers near the center of the map. It didn't seem to affect combat any, but was a nice visual. Kudos to that map-maker, who also made Horselands iirc, another excellent custom map. We (47Ronin) enjoyed many a late night MP battle on those.

Edit: diction fix