For anyone who might not know, an open mat is an open training session at which there is no organized instruction. Many schools host open mats, and of those many allow students of other academies to attend, sometimes with a decreased (or waived) mat fee. Given the way that BJJ evolves, and how information gets disseminated open mats can be a crucial way to learn and field techniques.
Another element to open mats is that you never know who will show up. I’ve been at open mats featuring multiple black belts and pro MMA fighters who came to roll, I’ve also been to open mats with only a couple of people and worked on different situational rolling. In regular classes you get a fairly predictable mix of activities, you never really know what to expect when you walk into an open mat, only that you’ll have plenty of time to roll.
Another aspect of open mat is that it allows you to go places you wouldn’t normally go and train with people you wouldn’t normally train with. You can always cross train by dropping into other schools but open mats are specifically intended for what their name implies: to be open.
There is something anyone who goes to open mats should be aware of: not everyone plays by the same rules as you may be accustomed to. I’ve had people reap my knee and go for heel hooks at open mats or get mad at me for going for wrist locks. In the back of your mind expect the unexpected. Different schools treat different submissions differently.
Go to more open mats and you’ll be better prepared for what people may throw at you at competition. If you step out of the comfort zone you’ve gotten used to at your school, you will begin to really know what techniques other people are studying, you gain a better understanding of the parts of your game that work and which ones you may want to consider discarding, and on an overarching scale you’ll really be gaining the full benefit of jiu jitsu. If you don’t, chances are you’ll miss out on a lot of this.