The characters are staging an ambush in a fairly narrow street, and will have been planning on having to neutralize enemies on horseback; these would be trained chargers; vicious horses that bite so just unhorsing the enemies is not necessarily ideal. At one point two cavalry will charge them, and I'd like to have them whip out something to cripple the horses (I like horses and all, but these characters aren't squeamish about maiming them, fatally or no.)
I have several ideas. I don't think a rope across the road would be practical, and I'm not sure exactly how a horse would react to caltrops; if they'd go straight down on the ground or just stop and limp, and I'm going for tripping them. Guns would have to hit just right to take the horse down right away, I think, and aren't really accurate at this stage of development, plus moving target. Someone else suggested a bola, but I don't think a bola fits the setting, it would be too specialized a skill for the characters. Hamstringing would be ideal, but I don't think a rapier would do it, since it's a stabbing weapon, and a knife is more for close quarters and would be risky, since the horse is likely going to try and kick on the way by. A poleaxe would probably work, except that it's not easily concealed under a cloak. I'm thinking a regular axe might work, but I'm wondering if there's something I'm missing?