I think your numbers are a bit off. As is, Arnold Schwarzenegger (Str 20) could punch me (Str 7), and if he rolled a nat 20, and I rolled a nat 1, he'd knock me back 50 ft. Even in high fantasy, that's a little much.
The following is excerpted from the revised rules from Four-Color to Fantasy: Modern Edition.
Knock-back
As an attack action, you may attempt a knock-back, similar to a bull rush, in which you use the force of your blow to knock an opponent backward or to the side, without having to pursue him. Though great strength is usually required to knock an opponent back like this, you must consciously choose to knock your foe back, regardless of your strength, since most hits do not provide enough thrusting power in a single direction to move your foe much.
Making a Knock-back Attack: You must declare a knock-back before you make your attack roll. Note that making a knock-back is an attack action in itself, so it cannot be made during a full attack action. Make your attack roll as normal, but if you hit, do not add your Strength modifier to your damage, since most of the force is being used to push back, not injure.
Then, make a Strength check, using your effective Strength for lifting, carrying, and throwing, as determined above. The DC of this Strength check depends on the size of your target.
Fine: DC 4.
Diminutive: DC 8.
Tiny: DC 12.
Small: DC 16.
Medium-size: DC 20.
Large: DC 24.
Huge: DC 28.
Gargantuan: DC 32.
Colossal: DC 36.
At the game master’s prerogative, the DC may be reduced for creatures that are lighter than their size would suggest, or increased for those that are heavier than average. A Large iron golem would probably count as a Gargantuan creature because of its immense weight, while a hollow Huge whicker monster might only count as Large for the purposes of moving it. Also, knock-backs do not work against creatures that are intangible, and the game master may rule that certain types of creatures cannot be knocked back because of their substance or structure. Air, fire, and water elementals cannot normally be knocked back, nor could a golem made of thin paper, since the mass of the creature is not solid enough to knock-back.
If you beat the DC of the target, you knock it back 5 feet, plus 1 foot for every point by which you succeeded, in the direction you choose. This direction obviously must be away from you, not toward you. You may choose to hit the target a shorter distance if you want. To determine how high the target flies, divide the total distance by four; this is the usual height of the target at the apex of its flight. When the target hits the ground, he takes 1d6 points of impact damage from falling and skidding.
If the target strikes a solid object before it travels its full distance, both it and the object it strikes take 1 point of damage for each foot of distance left. This is in addition to the 1d6 points of damage the opponent takes when he lands. If this is enough for the target to break through the object, he will keep flying, possibly striking more targets.
If the target thrown is smaller or larger than Medium-size, it takes the same damage from an impact, but deals one-half as much for each size category smaller, or two times as much for each size category larger.
Knock-back Tricks: Sometimes you want to do more than just send your foe flying.
If the path of your knock-backed foe travels through the square of another creature, that creature can choose to either try to dodge, or try to stop the flying creature. If the creature wants to stop the projectile, make an opposed Strength check against that creature, as if with a bull rush, including normal modifiers for size. Instead of your normal Strength bonus, use the remaining feet in the knocked-back creature’s flight as your bonus. If the creature succeeds its check, the knocked-back foe lands prone in that square, and takes full damage as if it had struck an inanimate object. The creature that blocked the flight takes no damage.
If it fails its Strength check, then both creatures fly along the same path as the first one. The distance they travel is equal to either the amount left in the original creature’s flight, or the amount by which you beat the interposing creature’s Strength check, whichever is less. Neither one takes any damage until they land or strike a solid surface.
If the creature wants to dodge, it must succeed a Reflex save (DC 10). If successful, then it avoids the projectile, and the knocked-back creature continues its movement. If the creature fails its Reflex save, treat it as if it tried to block the flight, and rolled a natural 1 for its Strength check.
You may also try to intentionally use your knock-backed foe as a ranged weapon, trying to deal damage. After you succeed in the knock-back, make a normal ranged attack roll (usually with a –4 non-proficiency penalty, unless you take Exotic Weapon: Punted Supervillain). Assume that a knocked-back creature has a range increment of 5 ft. This is not a touch attack, since you could strike and still not deal damage. If you successfully hit, deal damage the same way as if the hurled foe had struck an inanimate object. If you beat the touch AC, but not the full AC, the hurled foe takes full damage, but the target you were trying to hit takes none.
If there are creatures in the way of a deliberate ranged attack like this, then they provide a cover bonus to the target’s AC, unless those creatures want to dodge. Instead of having targets make Reflex saves to dodge in this case, simply assume that since you’re trying to avoid them, and they’re trying to avoid you, they don’t provide cover.
Throwing Foes: In order to throw a creature that is struggling, you must use a full-round action to attempt to grab and throw that foe. First, make an attack as if you were trying to grapple your opponent, with a –10 penalty. If you are successful, make a ranged attack roll, just as if you were trying to throw a log or something similar. You suffer a –4 penalty to your attack roll because your opponent is struggling, in addition to the –4 penalty from being non-proficient, unless you have Exotic Weapon Proficiency (giant ranged weapons). If your foe is paralyzed or unconscious, you do not suffer the –4 penalty from its struggling.
If you already are in a grapple, you can, as an attack action, make an opposed grapple check with a –10 penalty to throw your opponent. Then make a normal ranged attack roll, with the –4 penalty as detailed above.
Example One: A slumbering ancient wyrm gold Dragon is awakened when he senses a pair of kobold thieves stealing trinkets from his horde. Instead of crushing them in his lair and having to clean up the mess, the Dragon follows them until they exit his cave, then strikes, hoping to have some fun and play kobold golf. He easily succeeds a knock-back attack, and makes his Strength check against DC 16 (since kobolds are small). He rolls poorly, and gets only a 32, and thus punts the scaly thief 21 feet down the mountainside. The normal attack, plus the falling damage, easily kills the small brigand.
He chases after the second kobold as it screams and runs for its life, and this time does better, getting a Strength check of 46. With a pitiful wail, the kobold flies a satisfying 35 feet, and a new Draconic sport is born.
Example Two: While placidly playing with a group of street urchins, Zidi spots a giant Goblin charging the town’s walls. Her first attack – hurling a wagon at it – doesn’t take it down, and the Goblin is smart enough to send his normal-sized minions in first to soften up the Halfling Titan. Zidi doesn’t worry much about the small Goblins, but she can’t reach their huge leader, so she adopts new tactics.
With a fierce punch, she tries to knock a Goblin warrior into his leader. She easily hits, and rolls a 31 for her Strength check, enough to knock the Goblin the 20 feet to his boss. Unfortunately, there are too many other Goblins in the way, and after flying only 5 feet the hurled Goblin enters the same square as one of his comrades. The Goblin tries dodge, but fails his Reflex save, and is hit nearly completely off balance. The two Goblins could continue to fly 15 more feet, but there is one more Goblin right in front of the leader, who loyally tries to block his flying comrades. Since by this point they only have 5 feet of flight left in them, Zidi only has a +5 bonus to her opposed Strength check, and the Goblin manages to stop the projectiles. Both the Goblins that were flying take 1d6+5 points of impact damage from the landing, but the Goblin who stopped them is unhurt.
Peturbed, Zidi tries the next best thing the next round, and looks for a good Goblin to throw.
