The Roles, Rules and Rolls blog recently posted about making mundane animals properly dangerous. In the post it was mentioned that some games, like Melee, allowed two combatants to occupy the same space, rather than adjacent spaces methodically whacking each other with swords or clubs or whatever. Occupying the same space means an attacker is coming in close, effectively inside the range of most swords, axes, spears; in fact, most melee weapons in general. The only effective weapons at this range are unarmed attacks, natural weapons and melee weapons no larger than a short sword.
The nice thing about a rule like this is that it a) makes mundane animals scarier (since they benefit from their natural weapons while the PC is reduced to fighting with a dagger) and b) provides daggers, knives, short swords and similar weapons with a viable specialized role in combat, rather than just being back-up weapons. A wild animal gets into infighting range with you and your big two-handed sword is useless; you’ll need to draw a dagger and start stabbing.
So here’s my completely game-theoried, untested, probably bug-ridden infighting house rule for Pathfinder Core/BB:
In Pathfinder terms, I’d say that moving into infighting range (occupying the same space as your target) is a two-step process. First, you have to move up adjacent to your target normally. Then, as a full-round action (or standard + move action in the Beginner Box) on the following round you move in to infighting range and make your attack, perhaps requiring a successful Combat Manuever roll to do so. Naturally, moving this close to your opponent invites an attack of opportunity, as well. Moving out of infighting range has the same requirements and steps.
Optionally, you may say that all attacks made while infighting are CMB/CMD rolls instead of standard attack rolls. This accounts for the reduced effectiveness of armor at extremely close range, slipping daggers through gaps and eye slots, etc. In addition, it makes infighting appropriately impractical with large-sized monsters.
Of course, the Beginner Box doesn’t use Combat Manuever or Attacks of Opportunity. Typically, an action that allows an AoO in Pathfinder Core simply can’t be taken in the BB, unless you have the appropriate feats. Therefore, in the BB I’d say you can’t move into infighting range unless you have an appropriate feat, such as Acrobatic Steps or perhaps Combat Expertise (or, if using the Consolidated PFBB Feats, Unarmed Combat; alternatively, just make up a new feat called Infighting Combat and make it available to fighter-types and rogues). Animals are considered proficient with their natural weapons and so would be able to close to infighting range. The BB has no substitute or stand-in for CMB/CMD, so you’ll have to stick with standard attack rolls for infighting, with the restriction that melee weapons larger than a short sword cannot be employed.
To be clear, it should be noted that a character only needs the appropriate feat to initiate infighting. If someone else initiates infighting with the character they can still fight normally with daggers, short swords or similar weapons.
I think such a rule would be of greatest use with ‘mundane’ animals, such as wolves and bears, rather than NPCs or large monsters. It seems logical that most people would prefer to use their most effective weapon most of the time, so they probably won’t be rushing into infighting range at every turn. However, should a character lose their primary weapon, there’s a definite advantage to infighting, as it probably neutralizes the other guy’s most effective weapon, too. It’s also possible that a PC or NPC would choose to specialize in infighting combat techniques, for whatever reason (it would certainly surprise the PCs and throw them off their game a bit).