Are there sword forms that hold the sword in reverse grip or is it just hollywood/anime garbage
3 Answers
Overall, It Is A Silly Grip For Combat
Coming from a Historic European Martial Arts perspective, I can say this is "Hollywood/Anime Garbage".
Generally, you lose reach, leverage, and speed while you gain... dubious forearm protection and the scorn of your peers? Historians and enthusiasts on YouTube goes in much more detail. In short, it is just not as effective as forward grips in most situations.
What IS It Good For?
Against humans, there is a notable exception here: attacking targets already on the ground via stabbing. At that point, you have mostly won armed combat against humans, so this is pretty niche.
This reverse grip allows you to get a lot of body weight behind a thrust downwards, when the target is close. Maybe there is space for this when attempting to go hilt-deep into a massive creature or some sort of ankle biting foe, but is a sword a practical choice here? Especially when other ancient weapons have more reach, better leverage, and/or more force? (Like a staff, spear, partisan, club, etc...) This is really outside the scope of this (martial arts) site and I cannot really cover all fantastic settings.
But Daggers!
Using daggers in reverse grip is well documented and accepted. This is due to certain systems combining wrestling with the use of the dagger. These daggers are generally very robust and sometimes quite large, but the fact is that the closer you bind to your fist, the more power/control you can exercise. The majority of a reversed-gripped swords is generally too far/long to gain control in a bind or effectively move around in a grappling setting.
Techniques for swords in grappling usually demand you half sword, which is grabbing your own blade, or grab an opponent's blade, which is an entirely different way to hold a weapon. Even so, the dagger is usually better in grappling than a sword! (Why else would knights have daggers in addition to their swords?)
In theory, you could use a very short sword in the same way as a dagger, although this opens the "what is a dagger?" debate and questions about "can this technique be used with a blade of X length?" We do not have room for this here.
There really isn't a style of swordsmanship that uses it all the time, but there are situational uses for the reverse grip that are historically documented.
Fiore dei Liberi holds the sword in a reverse grip with the purpose of wanting to throw the sword like a javelin which Skallagrim has demonstrated before on his channel.
Historical Japanese and Chinese swordsmanship occasionally seems to show it used for certain situations:
And in iaido/iaijutsu it is occasionally done, but primarily as a method of returning the sword comfortably and also during very specific situations when the sword can only be retrieved in a reverse grip:
The reverse grip is especially important if you want to comfortably draw and sheathe an especially long sword since it will allow a tighter angle to be made when drawing/sheathing without putting too much strain on your wrist.
It also is occasionally done on particularly short "swords" like butterfly swords from Wing Chun and are a way to use your forearms as a blocking tool kind of like how a tonfa would work or as a method to use your swords at extremely close ranges where you would be throwing elbow strikes.
Keep in mind with all the examples given though; they are situational moves designed to supplement holding the sword the normal way and not something that is done all the time like seen in fiction-land. :P
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It's worth noting that the thrown sword technique is not really a reverse hammer grip like shown in the Asian sources. Fiore shows gripping the base of the blade (usually an unsharpened part) and not a full "reverse hammer" grip as the Asian sources. Modern interpretations sometimes have fingers hooked around the hilt, and most people do a sort of sideways throw. Commented Jul 12, 2022 at 17:22
Short answer is that, as discussed in this Reddit thread, there are no traditional sword forms involving a reverse grip, although some styles include occasional use of it on a situational basis (usually in service of hiding the blade, striking when you have your blade reversed to indicate that you are not holding it ready to strike, or your grip becomes reversed in the course of the swordwork (such as when the sword has been knocked out of your hand and the way in which you caught it was reversed). As to why it's not generally used, this fellow has a good explanation.
I will add my input as to why there is no style dedicated to it. For starters- it is completely predictable. You are limited to an up strike and one from the side. You can even manage one from the top, but that forces you to turn your body in an awkward way and not only tells your opponent exactly what you're doing, but you will not recover in time for a consecutive strike, nor will the initial one have enough force behind it. In terms of defense, since the sword is either facing tip down or across, you now have every vital position at risk with a faulty guard. It doesn't matter how strong your arms are, if the opponent takes a good whack, the guard will break simply due to physics.
Note: when I say "you" I mean generally; I'm not saying this in a convicting manner at all.