The one I quoted is a minor precept and it is about storing weapons, it is not about their use, but the fact that one possesses such tools. That makes it clear how even the potential of aggression should be removed. Regarding the acts of any form of aggression, it is covered by the major precepts. The acts of anger by the ninth, acts of harming and killing by the very first.
Yes, I understand that. That is why my point was that something like a kendo sword, or a kyudo bow, or a shotput, or a discus, etc. could be considered a "weapon" in the sense of the precept only through a tremendous stretch of imagination. These things are just no longer relevant in that manner, or taken up with any mind of harming others. Similarly, there are ritual implements that are originally (or in the form of) weapons as well...and one would not say that possessing these is an infraction, since they are not kept or used as
weapons for injuring beings. If we divorce "potential for aggression" from an object's actual use and the owner's intention for it, then kitchen knives, baseball bats, lengths of rope and anything else possibly useful for harming others would need to be abandoned.
Problem is, however, that as we easily identify with our body and acts have deep impact on our mentality, martial training generates a martial attitude. By learning defensive techniques you also learn to expect attack, you learn feeling insecure and afraid. Of course, if you can put that all down and maintain a peaceful and compassionate mind, there can be no problem.
"Martial attitude" as you seem to be expressing it here does not equate to how it is understood in martial arts, in my experience.
The result of learning defensive techniques, I have observed over many years, is not at all that one expects violent attack but rather that one de-mystifies and de-glamorizes human violence for oneself. Insecurity and fear are not commonly results of martial art practice, but rather the most common motivations for beginning
it. In practice one learns to relax and let these dissolve, not to engender or reify them...thereby ensuring that one's actions are never reflexively driven by them.
The most common result I have seen in accomplished martial artists is a greatly increased disgust with the idea of violent encounters, and a desire to resolve them - should they arise in one's presence - skillfully and with as little harm as possible to all parties (remembering also that the individual needing defense could well be someone else, not oneself).
Of course, if you can put that all down and maintain a peaceful and compassionate mind, there can be no problem. But then, why practice self defence?
Why? For the reasons I've mentioned.
I've practiced martial arts for 26 years. Every teacher I've had has said that the purpose of practice is to develop a peaceful and compassionate mind...and crucially, one that remains
so in situations of duress that test it.
To sum up: I am not saying that there are not martial-type activities out there that engender violent expression and should be avoided. There are. As I mentioned, there are also modern training methods for becoming proficient in the application of deadly force, and I'd stress again that we're not talking about those when using the words "martial arts".
But to make a broad generalization that "martial arts" are inappropriate for Buddhist practitioners is really just not useful. It may discourage some folks from taking up an activity that could really complement their practice rather than hinder it. There are many examples of practitioners who used martial arts positively in that manner. And in Buddhist practice there are certainly other examples of physical activities that would normally be considered infractions of the precepts being done, or simulated, or visualized in ways which support the intent of Buddhism...thereby transforming them into dharma assets. If martial arts can be used in such a way to transform violent mind, fear and attachment to the body - and at the same time cultivate energy, concentration, breath and posture - then who wouldn't benefit from them?