Mounted battle

From Wormhole Sci-Fi MUD Homepage

You can ride vehicles and some animals. You do this using the MOUNT command. While riding acreature or vehicle you can also fight, but those without the Mounted Battle skill will often find themselves knocked off. The skill is automatically used, if you know it and when you're mounted.

Those 'unhorsed' during melee combat lose any bonuses they derive from their mount (and leave it behind if they move, or recall).