Jens said:It doesn't make sense to me if you can hit twice as hard when spring attacking than you can when attacking without springing. So I don't think the original suggestion makes too much sense.
I interpret SA as allowing you to spring any time you take the attack action, ie you don't have to move before _and_ after the attack. So in practice, you would beable to use this new feat at any time (except during a full attack).
Alternatively, it could be altered a bit to resemble Rapid Shot (Rapid Strike: Req. BAB +11 and Whirlwind; make two attacks instead of one, both at highest attack bonus -2) with the obvious extension to Lightning Strike (req. BAB +16 and Rapid Strike; make three attacks instead of one, all at highest attack bonus -5). I have no idea if this is balanced, but my Rapid Strike should be equivalent to comrade raoul's Lightning Strike (-2/-2 is about as good as -0/-5). Lightning Strike is hopefully more powerful.
I think I like the Rapid Strike name, and the 0/-5 mechanic.

RAPID STRIKE
You are skilled at making fast attacks with a melee weapon.
Prereqs: BAB +11, WF, Dodge, Mob, SA, Expertise, WWA, Int 13+, Dex 13+
Benefit: When you take the attack action (not a full attack) with a melee weapon with which you have Weapon Focus, you can make an additional attack roll at a -5 penalty. You can combine this with other feats that make use of the attack action, eg Spring Attack.
Normal: You only get one attack roll when you take the attack action.
Special: You can take this feat multiple times. Its effects do not stack. Each time you take this feat, it applies to a different weapon with which you have Weapon Focus.
The iaijutsu master's One Strike, Two Cuts ability is basically Rapid Strike (katana).
(Why do people feel the iaijutsu master is broken, out of interest?)