In grappling martial arts and combat sports, particularly Brazilian jiu-jitsu, the word "guard" refers to a type of body position on the ground. In a guard position, one person (the one who "has the guard") is lying supine underneath another person (the one who is "in the guard") while the former restrains the latter with their legs. There are several varieties of guards like the "open guard", the "closed guard", and the "rubber guard". "Passing the guard" means for the person in the guard to escape into another position more advantageous to them. See the English Wikipedia article.
"Guard" in this sense seems to be well attested, with the earliest source I can find being a 2001 book called "Brazilian Jiu-Jitsu: Theory & Technique". According to other Wikipedias, "guard" also seems to be used in similar senses in German ("Guard"), Spanish and Italian ("guardia"), French ("garde"), and Hebrew ("גארד").
However, the word "guard" in this sense strikes me as strange: "guarding" usually means to protect, but in guard position, the person lying on the ground is not really protecting anything. And I cannot find any reliable source explaining the historical origin of "guard" in this sense.
Are there any reliable sources that explain the etymology of "guard" in its sense as position in ground combat? Is it supposed to be a metaphor or metonym?
Edit: Thanks for the comments. It's true that "guard" in English also can refer to watching over or staying close to someone to control them or prevent them from escaping. Even with this, it's still unclear whether it was from this meaning that this specific grappling position was named. (After all, "staying close to" could apply to any other grappling position, but it was this particular one that "guard" was applied to.)
In particular, because this term seems to be associated closely with Brazilian jiu-jitsu (the earliest extant source I can find using the term was that 2001 book), and Brazil's most common language is Portuguese, I'm wondering if there are any reliable historical sources indicating one of the following:
- That "guard" as a grappling position originated from Portuguese "guarda" in the new Brazilian jiu-jitsu community, before being transferred to grappling terminology in English and other languages. Maybe "guarda" is more idiomatic as a grappling position in Portuguese.
- That "guard" as a grappling position originated in English before being transferred to other languages.
- That "guard" as a grappling position originated from a language that is neither Portuguese nor English, such as Japanese. (I can find no judo term in Japanese whose literal meaning is analogous to "guard". For example, "ne-waza" / 寝技, which apparently means ground fighting, seems to literally mean "sleep" + "technique". Likewise, "do-osae" / 胴押さえ seems to literally mean "body"/"torso" + "holding back".)
I'm hoping for a reliable historical source or attestation that isn't just speculative. But I wouldn't be surprised if the answer is lost to history.