I seem to be riffing off of +Peter V. Dell’Orto a lot, but in this case we both got forwarded the same neat clip at the same time.
Peter made a lot of good points in his post. What I’m going to do is break down the iconic exchange in this video in roughly one-second intervals. And try and ascribe GURPS mechanics to them. I’ll use some screen captures to illustrate my point, but the entire video is also linked below.
Ready . . . fight!
We’ll pick up the action at roughly 2:46, where one of the featured interviewees ( Turns out it’s +Jake Norwood, HEMA fighter and author of The Riddle of Steel roleplaying game!) is talking about how points are scored. The real action picks up a few seconds later, with the red-socked fighter closing, and then starting the exchange.
The times given are in milliseconds!
The First Turn: 0-1000ms
|000 milliseconds – Time start|
At the point where I decided to start turn-based combat, we have Red-Socks (the combatant on the right) advancing to close the distance between the two fighters.
Red makes a deliberate advance – in fact, he does a step and attack, thrusting at his foe’s head. It would appear that, given the position of his foe at 0ms, he is starting from Reach 2.
|373 ms – starting the thrust|
By the time 373ms have elapsed, Red is making a very deliberate thrust for the face. He has advanced just about as far as he’s going to for the rest of the fight. In fact, one curious thing about this exchange of blows is that there is basically no retreating at all in terms of horizontal space. At this point, The defender on the left (identified as +Axel Pettersson by a commenter) has not exactly finished the parry, but it is well begun. The blade is sweeping to the defender’s right as it pushed the thrust in the same direction.
|594 ms – thrust is parried|
At just shy of 600ms, the thrust is fully developed and the parry is already in place, and it is continuing through the thrust so as not to bind the blade. It’s definitely the other fighter’s turn now, and he slides from that parry immediately into an attack of his own,
About an eighth of a second later, the fighter on the right has already committed to a swung attack to Red Sox left shoulder or left torso.
|723 ms – Initiate swung strike to red left arm|
One interesting thing here, that doesn’t really play in GURPS at the moment, is that it’s clear from the video that the defender did not have the time or the room to develop his parry into a thrusting attack. The sweeping parry that was used precludes that motion, so he’s got to deliver the swing – likely giving his foe a bit more time (but we’re talking about actions that are ticking by in 0.1s increments, so not that much time!) to defend.
|934mn – red parries|
Finally, at 934ms, the second attack of the first second has been launched . . . and is in the middle of being parried by Red Sox. The two fighters are still at Reach 1, where they’ll remain for the rest of the fight.
Notice that other than the first thrust, the parry turns right into the attack, with little hesitation or pause (at least this exchange). Also, following the high thrust, there was a high parry, a high counterattack to the left shoulder, and another high parry. Going high-to-low in one second probably is too much, perhaps.
The Second Turn – and the final one. 1000-2000ms
|1018 ms – disengage from parry and start swing to head|
We pick up pretty much where we left off, and as one might imagine, Red Sox does not surrender the initiative, and begins to develop an attack of his own.
He slides his sword out, disengaging from his parry and preparing to launch a head blow.
|1147 ms – head blow delivered . . . and parried!|
Note that from parry to disengage is 84ms by the movie capture clock. This stuff is happening fast.
By the time the clock ticks another 1/8 second, the head strike has landed . . . but already been parried by the fighter on the left, with a very strong parry. This may actually be where “the mistake” happens, as you can see that Red Sox has stepped to a more-or-less isosceles stance – the first time that has happened this fight.
|1363 ms – This doesn’t look good for Red Sox|
As the sands go through the hourglass here in bullet time, the fighter on the left has taken a strong offensive striking pose, while Red Sox is out of position and off balance a bit.
The two fighters’ blades are not in close proximity or contact for nearly the first time in this fight, and you can see – and Red Sox can sense – the advantage held by his foe.
|1528ms – Fatal Step Back|
Another 165ms ticks by, and Red Sox hesitates and begins to take a step back. Not a big one, but more importantly, he’s gotten fixated, perhaps, on protecting his head. Not bringing his sword along, it’s out of position and Red is off balance – this is even clear in the full-speed video. At this point (or maybe even two frames ago!) it’s probably all over but the bleeding for Red.
|1632ms – Opportunity knocks and White answers|
Our friend from Chicago (White Sox?) sees his opportunity and commits to it, a full-strength cut to the ribs. Still out of position and knowing it, Red tries to dance back – but it’s clear that he is off balance for a retreating dodge.
That being said, Red Sox does have this big sword thing over his head, and he’s about to realize it.
|1746ms – The fatal blow|
These last few frames are still very interesting,
though, since the end of the fight for one doesn’t instantly save the other. As the lethal blow lands, Red finds himself in a position to strike, if perhaps a late one, and commits himself to it.
White is stepping to his left, through the blow. and has not yet obviously committed or begun to any defensive action to finish the fight.
|1763 – Last-ditch attack, kneeling defense|
Only 17ms later, White is following through on his attack, while Red, despite having been struck (or while in the process thereof) is now attacking strongly to White’s head. He has recovered his stance (too late, alas) and is powering into a final blow.
|1967ms – Final Defense, game over|
You can see that White is starting to bring his left hand up, preparing for his guard stance. He cannot help but be aware of where Red’s sword was, and so he knows from where an attack must come.
And 204ms later, he has a very strong defense going, having dropped to one knee and completed his follow-through into that parry.
The point is over, a clear strike for white.
We’ll start with Red, obviously
Red: Step and Attack, a thrust to the head
White: Parry. 
White: Attack, perhaps Defensive Attack, a swing to the torso 
Red: Parry 
Red: Attack, a swing to the head. Maybe a Committed Attack? It would explain . . .
White: Parry 
White: Deceptive attack. Swing to the torso.
Red: Cannot parry; must dodge. This does not go well and he’s hit.
Red: The hit hasn’t registered with him yet, and he’s already made up his mind. Attack, Committed, to the head.
White: Drop to knees and parry 
 As noted above, that parry precludes a thrusting counter. This might mean that one can trade a bonus to parry an attack now for a penalty to your next attack. This is something mentioned in Option 11 of my old “MECE” post. It’s also likely the result of not being able to use a ‘fencing’ parry, which favors the thrust on both attack and keeping the blade in line for such during a defense. It may also be worthwhile to give flavors of defensive parries.
 Defensive attack because he can’t really wind up in a way that would say to me “yes, you’ve just doubled your penetrating power!” which is what swing basically does.
 Perhaps benefiting from his defensive attack, his parry allows him to clear the line well and deliver a strong attack to the head. He clearly strikes hard.
 White parries the attack to the head, and things go poorly for Red after this. For whatever reason. Red’s blade is out of position after this. The rules not allowing you to parry with the weapon you attacked with for Committed Attack would cover this well. So we’ll assume that’s what he did.
 At this point, White knows he’s been Committed Attacked. His foe must dodge. He also cannot retreat, which covers what happens next pretty well. White throws a Deceptive Attack to the torso, and Red must Dodge without retreating.
 White drops to a knee to successfully parry the last head blow, which suggests to me that doing that – dropping to a knee to defend vs. a high-line attack, should probably be worth the equivalent of a retreat. So if you drop to the knees during a defense – a Kneeling Defense – you get +2 to your Active Defense against a blow to the arms, torso, or head. You do not have to step.
Of course, given how things flow together, it may be that this move was just a sideways retreat, but giving a full +3 for a sidestep and posture change seems OK to me.
The only thing that would prevent this from happening in GURPS RAW are a couple of tweaks due to certain types of attacks not being allowed, and the fact that at reach 1 after a parry, you can still develop a full-power attack. Or maybe not. Maybe Committed or All-Out Strong attacks are the full “don’t get in my way,” and the type of decisive and fast swing we see here works fine.
It doesn’t change my thoughts about “only use thrust” damage, though. It also seems to emphasize that Trained ST (adding a bonus to ST based on skill) is perhas as true, or more true, than a big huge muscular guy being able to just do that much more damage with this kind of blow. Maybe you only get swing damage if you AoA at full reach!
In any case, these guys could probably not keep that pace up for long, which makes The Last Gasp look pretty good in terms of the Action Point economy.