The skill system in Adventures Dark and Deep (based on that developed by Gary Gygax for Castles and Crusades, published under the OGL) allows for the development of such cool moves by a game master, and I thought the following example from my own Erseta campaign might be a good illustration of the concept. Basically, one spends experience points in order to get a level in the skill, and further study gets one additional levels in the skill.
The x.p. cost is given below, and is multiplied by the skill level being sought. If the character's highest attribute is the one given first in the "base x.p. cost" line, he can use that cost. If not, he uses the "all others" cost. Ties count, so if your fighter has a 16 STR and 16 DEX, he can buy the "My Blade is a Reed" skill for 4,000 x.p. If that same character had a 17 STR and 16 DEX, he would need to spend 6,000 x.p. per skill level.
Using the skill requires a successful roll on a d20 against the relevant attribute, with bonuses if you have more than one skill level (-2 per level). Easy peasy. In my campaign, certain skills are only available if one's character takes the time to actually seek out those who can teach them, and spends the money, time, and experience points to gain the skill. Not so easy, sometimes, because there's no guarantee that a teacher will take any jackanapes that walks through his door with a bag of gold!
The city-state of Chevis prides itself on its fighting schools. Lords, princes, and kings send their scions to such schools to be trained in the deadly fighting arts that they teach, and regular knights and warriors dream of one day amassing sufficient wealth to study there. Other cities have such schools of course, but those of Chevis are regarded as the best of the best (albeit usually not by the masters and students of other schools in other cities!), and each is noted for a particular style of fighting. Note that these skills can be learned by characters of any class, not only fighters and cavaliers. Here are three prominent fighting skills taught by some of the preeminent schools of the city. Needless to say, the competition between the fighting schools of Chevis is intense indeed; the right to be called "the best of the best" is jealously guarded.
My Blade is a Reed
Base x.p. cost: 4,000 (dexterity), 6,000 (all others)
Make skill checks against: dexterity
This skill emphasizes the art of parrying with a sword blade, in order to draw a strong enemy in and gain advantage thereby. It can only be used if the character is wielding a sword of some sort other than a two-handed sword. At the beginning of each round, a character with this skill can declare that they are employing this style. If the DEX check is successful, anyone fighting the character with a weapon (of any type) will receive a penalty equal to twice his STR bonus "to hit". Thus, someone with a STR of 17 would actually get a -1 penalty "to hit" rather than the +1 he would normally receive. Additional skill levels will add an additional penalty of -1 per skill level to the enemy's roll. There is no penalty if the character attempting to use the skill fails his DEX check; he can still attempt to use the skill on subsequent rounds.
Base x.p. cost: 3,000 (strength), 5,000 (all others)
Make skill checks against: strength
This skill emphasizes the channeling of physical strength in order to overcome the defenses of others. It can be used by a character wielding any sort of weapon. It can be used by a character wielding any sort of weapon. At the beginning of each round, a character with this skill can declare that they are employing this style. If the STR check is successful, any "to hit" bonus the character would ordinarily gain from his STR score is increased by 1. Further levels of this skill will increase the bonus by an additional +1. This skill will not work unless the character in question already has a "to hit" bonus due to strength.
This style of fighting is taught by the Morfino School of Chevis. The current Maestro of the school is Tormano Nosca (F15). Entry to the school requires that potential students impress Maestro Nosca in a contest of grappling. His strength score of 18/13 makes this a relatively high bar to pass. This skill requires 5 weeks to learn, costing 1,750 g.p. per week per skill level. The colors of the school are purple and black.
The Death of a Thousand Cuts
Base x.p. cost: 4,000 (dexterity), 5,500 (all others)
Make skill checks against: dexterity or strength
This skill teaches the art of wearing down an opponent by eschewing opportunities to deal killing blows in favor of inflicting a flurry of smaller, minor wounds that end up laying one's opponent low. It can be used by a character wielding any sort of edged or pointed weapon. At the beginning of each round, a character with this skill can declare that they are employing this style. If the skill check is successful, the character gets twice as many attacks as he normally would in the round, but each is made with a damage penalty of -3. It cannot be used in conjunction with weapon specialization.
This style of fighting is taught by the Chorvosa School of Chevis. The current Maestro of the school is Giovano Hech (F13). In the last few years, the school has fallen on hard times financially, and Maestro Hech has opened up the doors of the school to any who have the tuition (he is unaware that it is Maestro Nosca of the Morfino School who has subtly manipulated Hech's investments over the last year or so). This skill requires 8 weeks to learn per skill level, costing 1,500 g.p. per week. The colors of the school are red and black.
NOTE: In the World of Greyhawk Fantasy Setting circa 576 CY (or later), these schools could be said to exist in any major metropolitan locale such as Rel Mord, Rel Astra, or Zelradton.