Beowulf Rolls a 1

Wiglaf hearing about Beowulf's 1.
J.R. Skelton (1908)

Something of a shower thought, this one.

If a 20 is ruled/house-ruled as a crit, it often follows that a 1 is a fumble.

Very reasonably, higher level Fighters complain that this means they end up fumbling more often than less-skilled characters.

When a non-Fighter rolls a 1 to hit, it's a fumble, and they drop/break their weapon or wound themselves or trip over an imaginary invisible turtle.

When a Fighter rolls a 1, it's goddamn heroic:

• At 1st level, they break their weapon (causing normal damage) and all unlevelled and max. 1 HD/level monsters/NPCs who witness it must make a Morale Check.
• At 4th level, they break their weapon (full damage) and all max. 3 HD/level monsters/NPCs who witness it must make a Morale Check; unlevelled and lower than 1 HD/level NPCs/monsters auto-fail the Morale Check.
• At 8th level, they break their weapon (crit/double damage) and all max. 4+1 HD/level monsters/NPCs who witness it must make a Morale Check; all max. 3 HD/level monsters/NPCs auto-fail their Morale Check; unlevelled and lower than 1 HD/level NPCs/monsters auto-fail their Morale Check and must save or be rooted to the spot in awe/fear for d3 rounds.

Alternatively (or in addition), instead of the Morale Check on witnesses, you could bestow some later edition Barbarian Rage on the Fighter (1 round at 1st level-3rd level, 4 rounds at 4th to 7th, 8 rounds from 8th).

This should be enough to pull off a monster's arm or wield a giant-forged sword.

Magic weapons can be exempt from this rule, although I'm happy to see them shatter. Furthermore, the heroically shattered weapons of 4th and 8th level Fighters make suitable materials for making other magic items/weapons (cf. Narsil/Anduril).

As a general rule, if a monster can only be hit by special and/or magical weapons it's not likely to be affected mechanically even if the broken weapon is magical. 

At lower character levels and/or lower-magic settings, a non-magical weapon broken on a 1 could be ruled to cause to damage to otherwise invulnerable monsters and be eligible for re-forging as a magical weapon.

Commentary.

This is because of Beowulf, but he's not the only one to break a sword on the hero's journey.

Beowulf as foundational fantasy rpg text, via The Lord of the Rings, and as an OSR exemplar via The Eaters of the Dead/ The Thirteenth Warrior.

In a combat-focussed d20 system, this is going to happen often enough to add a dimension of the ridiculous - so you could either a) save it up for narratively significant fights or b) boringly make non-Fighters fumble on a 1, but Fighters only miss.