Can you “backstab” with a siege weapon?

Question

The 2002 movie The Gamers has a famous scene where the party's thief backstabs someone with a ballista.*

The movie uses a vaguely Dungeons-and-Dragons-ish system. Would any of the versions of D&D that existed at the time (2002), as written, permit someone to backstab (or that edition's equivalent) with a ballista? In other words, how accurate was this scene's joke at the time?

^{* In the video it looks more like a large crossbow, but since they treat it as a ballista when looking up the rules this question is about a ballista regardless of the prop used.}

Answer 1

The following omit an assessment of the difficulty of succeeding on a backstab with a ballista, and, instead, only attempt to determine if such an attack is possible.

• "Back stabbing is the striking of a blow from behind, be it with club, dagger, or sword," says the Advanced Dungeons and Dragons Player's Handbook (27). According to the Dungeon Master's Guide, although it usually takes a crew of 2 to operate a ballista, a smaller crew only reduces the siege weapon's rate of fire, and no weight is provided for the ballista. This means a generous DM could allow a backstab with a ballista (by interpreting blow as attack, ignoring the examples, and house ruling the ballista's weight to manageable), but I am certain Gygax would be displeased.

• The Player's Handbook for Advanced Dungeons and Dragons, 2nd Edition never explicitly says that a backstab must be with a melee weapon, although a melee weapon is strongly implied:

  Thieves... are masters of the knife in the back. When attacking someone by surprise and from behind, a thief can improve his chance to successfully hit... and greatly increase the amount of damage his blow causes.

  The multiplier given in Table 30 applies to the amount of damage before modifiers for Strength or weapon bonuses are added. The weapon's standard damage is multiplied by the value given in Table 30. Then Strength and magical weapon bonuses are added.

  Backstabbing does have limitations. ... [T]he thief cannot use it on every creature. The victim must be generally humanoid. Part of the skill comes from knowing just where to strike. A thief could backstab an ogre, but he wouldn't be able to do the same to a beholder. The victim must also have a definable back (which leaves out most slimes, jellies, oozes, and the like). Finally, the thief has to be able to reach a significant target area. To backstab a giant, the thief would have to be standing on a ledge or window balcony. Backstabbing him in the ankle just isn't going to be as effective. (57)

  In Player's Option: Combat and Tactics a light ballista costs 200 gp, weighs 100 lbs., and

  can be aimed at any target in sight, provided the weapon is fully crewed. A light ballista with a partial crew can fire at single creatures of Large or greater size. [Note: The light ballista has a crew of 1; make of that what you will.] ...Any ballista's field of fire is limited to 45 degrees left or right of the weapon's facing at the beginning of the round. A ballista's facing can be changed up to 45 degrees during the last phase of any round when it fires.

  However, a strong implication doesn't bar the practice, so a generous DM could still allow a backstab with a ballista.

  (Also, in both cases, a back stab or backstab multiplied only the weapon's damage. Thus dealing 264 points of damage—even with a ×3, ×4, or ×5 modifier to weapon damage—is extremely difficult.)

• When The Gamers was released, Dungeons and Dragons, Third Edition was still new, having yet to transition to Dungeons and Dragons 3.5, and the edition eliminated the term backstab (and, for that matter, thief). A Third Edition rogue straight from the Player's Handbook at level 1 gets the special ability sneak attack instead, which can explicitly be used with a ranged weapon against an unaware foe or against a foe at a battlefield disadvantage. The Third Edition Dungeon Master's Guide lists no weight for the ballista, but gives the siege engine's cost as 500 gp and lists its crew as 1 (151).

Thus, of the three editions listed here, Dungeons and Dragons, Third Edition has the least controversial way to, essentially, backstab with a ballista. Even though the ability was no longer called backstab, it's common for gamers to refer to newer editions' mechanics by the mechanics' traditional names.

Answer 2

Question from the text of the question is:

Would any of the versions of D&D that existed at the time (2002), as written, permit someone to backstab (or that edition's equivalent) with a ballista?

If "as written" means "was this a RAW compliant attack" the answer is NO, due to the damage being far too great for a single ballista shot: 264 points of damage. If that isn't the question, and the question is "can you sneak attack with a ballista" ... that's another matter explored below.

The DM allowed it, so the answer to the title question is obviously "yes," if the game being played was AD&D. The imbedded question (quoted in this answer) asks about versions in print at the time the movie was made. AD&D 1e and 2e were in print at the time.

With the understanding that the game may have been a version of AD&D, versus GURPS or something else, the question is then "Which one?" and the true answer to that is: unknown.

Why this might have been an AD&D 1e or 2e Setting

• The DM could have exaggerated for effect.

• The DM could have been using a critical hit table. (Common among AD&D 1e DMs even though non within the rules)

• The DM could have been amused and chosen to go dramatic for narrative effect. (Rulings not rules approach to DMing, endorsed in writing by the game's author).

Rulings, not rules. Under that basis, this could have been a representation of a 1st or 2d edition AD&D game, since the DM could allow all of the above, and could have chosen to inflate the damage for dramatic effect. These are good enough reasons for a DM to allow a ballista back stab.

Reasons To Not be AD&D First Edition is RAW based, not Rulings based

1. Small note: the book the DM consulted didn't look like the 1e DMG, nor the 1e PHB, in terms of what the brief view over his shoulder offered. This leaves 2e or 3d as more likely.

2. The backstab and triple damage for attack from the rear cited in the scenario (level 5-8 thief) would fit the 1e model(PHB, p. 27), as well as the need to catch Hunk by surprise to achieve that back stab bonus for damage and +4 to attack.

   • The original backstab by rules as written wouldn't apply with a ballista. The rule for that sort of attack (p. 27 PHB) cites an attack by "club, dagger or sword."
   • That said, Unearthed Arcana expanded the thief's weapons to some bows, but it did specifically list, in RAW, the ballista (which is a siege weapon) as a thief's weapon available for choice.
   • The DM's "there isn't anything against it"¹ (besides taking almost no time to consult the book, and thus being very unrealistic) looks like a decision that a ballista was a form of crossbow and thus a weapon of proficiency eligible for that backstab (the DM's I played with did not give that damage multiplier for bow shots and ranged weapon, but a DM could apply the logic of "now that bows are thief weapons, all thief attacks can be made by all thief weapons)."
   • We don't know what class this thief actually is. If he were a Fighter/Thief, or a player with two classes (some Fighter and most Thief), then weapons restrictions are moot since fighters can use ANY weapon.

3. The amount of damage finally ruled by the DM, 264 points, argues heavily against an AD&D 1e setting if RAW is operating (likewise for AD&D 2e and D&D 3.0). For that siege weapon, per DMG p. 108, the damage is 2-12 for man sized and 3-18 for larger than man sized for the roughly spear sized projectile. Triple Damage, even on 3-18 base, won't reach 264 points any time soon.

4. Insofar as maneuvering a ballista, all the thief needs is a belt of Storm Giant strength, or something similar (RAW available), and he'd be strong enough to handle it with some grace and even stealth. How he got that siege engine into the bar into the first place is a matter left unanswered in the film. The plus to damage from that belt, +12, while it should not apply to this missile shot, would still not, even if tripled, boost the cited damage into the range reported by the DM.
5. To mitigate "can the thief use that weapon?" the thief could use that weapon even in a case of non-weapon proficiency (-3 for thieves) being applied to offset the +4 for a surprise attack from the rear. Since the DM rolled a hit, that all comes out in the wash.

Summary

Even though the rules as such don't explicitly seem to support a ballista backstab and that much damage, the GM can allow it in 1e. In 2e, ranged weapons could be ruled as "backstab" inclusive, but the text does not explicitly say so, thus 2e may be in play.

All of these points are irrelevant if "as written" is the key criteria: none of the three editions would produce that much damage (264 points) from a sneak attack/attack by surprise from the rear, even with a ballista.

In that sense, if the question is "can this be done with rules as written" NONE of the D&D versions in print at the time apply since the damage is so far beyond what that weapons does as to beggar belief -- which seems to be the point of what's going on in the scene, a case of exaggeration for dramatic effect.

The DM ruled that it did more damage than it could. In that sense, the AD&D versions that emphasized rulings over rules (1e or 2e) is the more likely candidate for being the version in play.

¹ We don't actually know that he consulted a rule when he opened the book. That might have been him stalling for time as he thought through this ludicrous situation. If he DM'd like some of the DM's I played with, the more outrageous the idea, sometimes the more amusing and entertaining it is for the DM. I made a lot of off the cuff rulings when I dm'd since I did not like slowing down play when I could help it.