According to experts from the Technical University of Munich, Germany, squeezing a soft ball or making a fist with your left hand could help combat sporting nerves.

(Basically when we practice a particular movement thousands of times, it becomes automatic and requires little conscious thought, by shifting the balance of brain activity away from the left side, which governs conscious movement, and towards the right, which is key to automated behaviour, we can reduce the likelihood of choking under pressure and because each of our arms is connected to the opposite side of the brain, this can be done by clenching the left hand.

Now, two thoughts come to mind.  We should test this theory the next time England needs to take a penalty, and I wonder if clenching the right hand can reduce exam nerves.)