A lot of our class rules coincide with the competition rules for IBJJF tournaments. Here's a link to the IBJJF Rule Book v4.0 in case you're curious but if you've just started Jiu-Jitsu you may want to wait to thumb through it when you've had a couple of months of training. This PDF might be more helpful as a quick guide: Technical Fouls & Illegal Moves Poster (pdf)
That being said there are a lot of different types of tournaments and rule sets and we'll often modify our training based on the upcoming tournament's rules. Whether that's for points, submission only, gi and no gi, ADCC, no time limit, combat jiu-jitsu, etc.
Remember while it is a combat sport and martial art, we must take care of our training partners. A common expression is "don't break your toys." We want everyone to avoid injuries and be able to train as often as they can. Furthermore, knowing when you need to tap is paramount.
Techniques that are prohibited for everyone:
Slamming or throws that puts your partners head/spine in danger (suplex)
A common example of slamming is having a person in your closed guard, standing up, and then dropping them to the ground with force and landing on top of them. There are videos on youtube that are titled "How to get DQ'd in BJJ" It is a very dangerous technique and can cause damage to your training partner's back, neck, and head.
That said, we should not ignore it completely and learn how to defend against a slam. Whether it's self defense situation or you are rolling with someone that isn't familiary with our rules it's good to protect yourself. Here's a decent video with some options: How to Not Get Slammed in the Guard
Small Joint locking (Fingers and Toes)
You are not allowed to grab individual fingers in order to escape a submission or in the process of attempting your own. You may grab all of the fingers together, but any single digit manipulation is not safe for your training partner.
Techniques like eye gouging, fish hooks, hair pulling, groin strikes, biting, etc.
These are probably obvious and I'm probably missing some. Again for self defense purposes we should be aware that these things can happen, but they have no place in our average class.
Heel hooks and reaping the knee in the Gi
The heel hook is one of the strongest submissions in BJJ and has found some popularity lately in sub-only no gi events. It is a general rule in Gi BJJ tournaments that heel hooks are not allowed along with reaping the knee because of the added friction the gi provides.
Prohibited techniques for white belts specifically
- Wristlocks: Any pain compliance techniques using the wrist
- Twisting Ankle Locks: Toe Holds, Heel Hooks, Estima Locks
- Knee Bars
So that would imply the techniques above are fine for blue belts and above. I would still stress some caution when it comes to new blue belts or other blue belts you don't normally roll with or visitors to the club. It's perfectly fine to ask, "what do you think about toe holds and knee bars?" as you slap and bump before the roll. Once you've established that you and your partner are both good with them, then it's probably fine to use them in future rolls.
Reminder that heel hooks and reaping are not allowed in the gi at any level, only no gi.
Also it's good to keep in mind that many of these techniques are still not allowed in tournaments that you might compete in, so get familiar with the rules of the tournament you are preparing for.