Keep in mind that most (European) armies of the time considered it dishonorable to shoot at officers. The Brits were terribly disappointed in the American colonists who insisted on picking them from their horses at range.

With that in mind, the falling off the horse suggestions make the most sense. Here's another in that vein. Have them shoot (or stab) the horse out from under him. One of the common problems of the day was having the dying beast fall on top of the rider. having a horse fall on, say, your leg as you're trying to disengage the stirrup would put you in a right pickle, waiting for the pursuing troops to lift the animal off of you and take you prisoner.

Depending on the ground, the fall might or might not break the leg beneath the horse. An unbroken but badly bruised leg or twisted ankle would be very painful and certainly inhibit movement, but would not be as debilitating as an outright break. The character would be able to hobble away. The ankle wound would also allow the character to ride, where the bruised shin or leg might not.