Weapon speed factor (WSF) (or simply “speed factor”) is a property of a melee weapon.
When initiative is tied, WSF comes into play. Attacks are resolved in order of weapon speed. In this case, individual attacks must be ordered, not attack routines, since an attack routine could consist of a main-hand weapon and an off-hand weapon with different speeds.
Bonus attacks due to WSF only occurs when the opponents are attacking on the same segment.Ex Therefore, in cases where one side has more attacks than the other side due to being a fighter, or haste, or whatever, bonus attacks due to WSF may not occur even if the initiative is tied and the opposing weapons would normally allow it.
For example, imagine a 9th level fighter with a halberd attacking a goblin with a dagger. The initiative is tied, but it is an odd-numbered melee round so the fighter gets two attacks, one before the goblin and one after. Therefore, the fighter's attacks do not occur on the same segment as the goblin's attack, and the goblin does not receive bonus attacks from WSF.