JWBL/BroB:FIrst of all, what does the bible say on the subject?
We have Isa.2:4 - the context being a future time of peace when war will be learned no more because there will be no more need of it. The passage wasn't talking about the contemporary time, which were violent times in which the Israelites continued to "learn war", as evidenced a few years later in Neh.4:17, 18.
The Psalmist David, a man of war and "a man after God's heart" (Acts.13:22), wrote Ps:11:5 - the context is the wicked, who enjoy hurting people, especially hurting "good" people. The context also shows that God has no compuncture about using violence against these ones.
Coming to the New Testament, there was no new law given. Matt.26:52, 53 should likely be read in the light of Joh.18:11, 36, meaning that it applied only to himself in regard to what he had to do at that time. You don't see him showing any such compuncture in refraining from warfare in Rev.19:21
In Luke 22:35-38 Jesus tells the disciples to arm themselves for self-defense.
Paul wrote in 1Tim.4:8 that bodily training is beneficial for a little, but godly devotion is beneficial for all things, as it holds promise of the life now and that which is to come. However he never condemned bodily training, which likely included various sports found in the olympics, like wrestling.
Paul also didn't hold back from using analogies that compared the spiritual fight to warfare, complete with weapons. It seems he had a keen interest in learning about such aspects of warfare, despite the passage in Isa.2:4.
So we actually only really have three passages of scripture which can be interpreted to being anti-self-defence-tuition, these being Ps.11:5; Isa.2:4; Matt.26:52. The context both within the passage and within the whole bible shows that such an interpretation flies in the face of the rest of scripture.
Even the golden rule "do unto others as you would have other do unto you" can be applied here. If you were violently attacking someone in the street, wouldn't you want them to defend themselves? Truly if you "love your neighbour as yourself" you would hope that they would not let you get away with such an illegal activity by passively letting you kick the living shyte out of them, and then calling 911 through toothless lips!
To use WTS-speak for a moment:In the light of these passages of scripture it would seem reasonable to conclude that self-defense classes are acceptible for Christians, as we keep on "buying out the opportune time ... because the days are wicked" (Eph.5:14-17).
BJJ sounds pretty cool.
I practice TaiChi for health reasons, which in mainly non-contact, except for "push hands" which has no strikes, grapples, chokes, or throws.
The WTS doesn't agree though. It disagrees with all forms of self-defense training/sport, and a number of recreations like bungee jumping. Depending on your local body of Elders there are many sports which would also cause problems. I was effectively invited to desist from Scuba diving before they would appoint me as an Elder. After I made it plain that I had stopped (I used to be an Instructor) I was immediately appointed at the next C.O. visit.