The scene occurs fairly early in the movie, and it introduces the sword expert character. Basically, there are two samurai, one boastful, one quiet, and the boastful one challenges the expert to a duel with wooden swords. After the duel, the boastful one claims it was a tie, but the expert says that he won. The two duel again, this time with real swords. When they cross swords, the two samurai stand for several seconds after they connect, and then the boastful one falls dead.
This scene of two swordsmen running at each other, connecting, and then standing in dramatic poses for a few seconds before the loser falls has been copied hundreds of times in popular culture both in Japan and worldwide. I think I've seen it in two different anime this week alone. Was this scene an original idea from Kurosawa, or did it come from another Japanese movie, manga, or Hollywood?
Kurosawa was influenced by John Ford's westerns. (Here's George Lucas on the subject.) So you might want to look at old westerns for your influences -- in particular the trope of the quick-draw gunfight, where both men shoot at the same time and then freeze, and for a few tense seconds the audience doesn't know what's happening, and then one of them falls dead.
The same duel is fought by Yagyu Jubei Mitsuyoshi, alleged founder of the Yagyu school of fencing.
This story became the basis for Kurosawa's scene.
Read it here in a google pages view of this book:
Traditions: Essays on the Japanese Martial Arts and Ways
By Dave Lowry
You will notice it is an exact copy of the scene, except for the absence of the Daimyo offering judgement that concurs with the aggressor, that it was a tie.
Whether this storytelling device exists prior to him, I have no further info on the matter.
Allow me to edit by stating that Yagyu's tale is in the early 1600's. so this may be the first of it.
You might want to ask in /r/movies for a more specialized audience.
The Criterion Collection of Seven Samurai features a commentary track by an expert in Japanese film. When discussing this scene, he doesn't mention any influences or precursor scenes. In general, the commentary focuses on the fact that pretty much every narrative, visual or editing technique used by Kurosawa in this film was the first example of its type.
IMHO, the scene probably owes more to traditional samurai artwork than anything else.
The clips in question (found badly on youtube)
the beginning https://www.youtube.com/watch?v=ldInjZY6fEI
and climax https://www.youtube.com/watch?v=kEYnLUhTn0Y
There's a more lighthearted version in Don Quixote, dating back to 1615 (publication date of the second book).
An enthusiastic but untrained swordsman challenges an expert to a mock duel. The expert parries his thrusts and touches the buttons on his shirt to mime critical hits. The reveal at the end of the fight is that the shirt is in tatters (similar to the samurai scene). The scene ends with the amateur admitting that skill matters in swordfighting.
There's a good chance that Cervantes was drawing from chivalry tales that provide inspiration for much of his book.