"Swing Stabs" refers to stabs that are swung directionally, usually in an arc-like fashion. The stab begins aimed away from the targetted player in a specific direction, and then at its apogee, the stab is directed towards the target. Swinging stabs directionally in this manner elongates the stabs in both time and space - swing stabs have a farther reach (see: ghostreach) than stabs directed right at the target.
There are four separate directions of swing stabs: up, down, left and right.
Left swing stabs are most commonly referred to when a side swing is discussed. This stab is performed by directing the attack towards the left side (facing) of the opponent. This usually causes the attack to create a difference in timing, causing a second or two delay in time between the start of the swing and the hit. Often the attack is aimed at the end or just past the end of the opponent's musket while he's blocking and slightly swung over - however, the attack may be aimed at any distance away from the opponent, and as long as the attack hits properly it will create a delay.
Attacks swung to the right of the player hitbox are the hardest to accurately land, as the nature of the bayonet and player meta creates a tendency to hit the player on the left side of their body. Without careful practice and mouse movement, the attack will either miss to the left or to the right. The side of the hitbox that the right swing attacks is harder to hit, but that disadvantage is traded by the fact that the right swing attack attacks faster than the other two swings, having the shorter distance to travel.
Up swing stabs are stabs that are thrown initially above the target's head, and then brought down to the target. These stabs are extremely technically challenging, as the nature and height of a moving hitbox are difficult to predict. These stabs are rare, but when pulled off correctly are virtually guaranteed to register.
Down swing stabs are stabs that are thrown towards the grown and pulled back towards the target after reaching the apogee. It is uncommon to see these stabs thrown directly forward - most down swing stabs are thrown in conjunction with a left swing stab.