The main reason for being tense is fear of the unknown (and the attempt to make up for the technique they do not have or the practice they haven’t put in). The desire to put up a good fight with hopes of impressing someone. Being so tense slows you down and makes you less aware of what you’re doing.
Slow down your movements, become more observant, observe and study the score move. Stop searching for submissions and you will find them in no time. “If your goal is to become comfortable in all positions so you can relax and learn faster, you need to first believe that the worst thing that can happen to you is that you will be submitted. If you have a problem being submitted, you are in the wrong game!” Roll with an awareness and admiration for the techniques and study and observe the technique of others. With this approach you don’t explode out of danger, you allow yourself to be defeated and learn the set up that got you in trouble so the next time you can defend a few steps earlier.
Keep it playful. Everyone who plays piano would like to play piano forever. Practice at a pace that allows you to play forever while increasing your skills of interpretation and performance. The only way to grow forever is to start playing…winning and losing are secondary because you are growing. The mind is like a sponge, but it must be open and willing to accept the information presented to it. If I am submitted it is not because I did something wrong but because my opponent did something right. Not tensing and allowing relaxation and awareness, the student also limits injury potential and can train longer.
The long term practice of anything. Don’t train. Play.
Think about how often people say they wish they’d kept up with lessons or knew how to play the piano. Use children to remind you to keep it playful, and teach them to keep it playful.
“To appreciate the art to a level that when you start being defeated by people you expected to defeat, you still smile.” Knowing when not to move is as important as knowing when and how to move.