Single Weapon Style

Single-Weapon style means that the character wields a one-handed weapon in one hand and nothing in the other. Though in real life this type of weapon use is often at a disadvantage compared to many of the others, it's very popular in film and fiction, and so it has some virtue in the game.

Advantages

The advantage of single-weapon style in the AD&D game is that the character keeps a hand free for Grappling, for switching weapons, for surprise maneuvers, for whatever comes along in the course of combat.

For instance, two fighters are going at it, and one Pins the other's weapon, the single-weapon fighter can use his free hand to perform Punching maneuvers; and he can try to perform barehanded maneuvers.

Disadvantages

The main disadvantage to this style is that the character does not gain the benefit of a shield's AC bonus.

Style Specialization

If the character devotes a weapon proficiency to Style Specialization with Single-Weapon Style, he gets a +1 AC bonus when using any one-handed weapon (for which he has proficiency) in Single-Weapon Style. He doesn't get the bonus if he carries a shield or weapon in his off-hand.

Additionally, he can devote an extra proficiency to Single-Weapon Style and have a total +2 AC when fighting in this style. That's the limit, though: He cannot devote more than two proficiencies (for a total of +2 AC) with Single-Weapon Style.