My personal take on batchalls is to ignore them except as a RP element. Especially when they present an impossible or thoroughly unbalanced situation like warships vs. infantry; even Clan "honor", dumb as it can be sometimes, must have some kind of rules about such a situation. Thinking practically, the warship could bombard hell out of the planet, but it can't take it by itself. So the infantry spreads out and digs in to survive the bombardment, and ends up still holding the planet and the challenge hasn't accomplished anything but wasteful destruction, which (supposedly) is totally against Clan ideals. From a RP standpoint, I imagine such an unbalanced challenge would come down to either one side conceding, or representatives of the two aggrieved parties (like the unit commanders) having it out in some way; pistols at twenty paces, WWE steel cage match, whatever.
In gaming terms, I would just create a fair battle using normal BV rules between relatively competitive unit types, and push the Clan RP crap into the background where it belongs. "Yeah, there was a batchall, and it came down to this star of Hell's Horses vehicles vs. your Mechs. Maybe you shouldn't have called them jalopies in front of their Khan, neg?"
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Be careful what you wish for. I might let you have it.