Back sticking, as the name implies, is the act of quickly switching from playing normally to swinging the stick around so that the butt of the drumstick hits the snare. This is a common trick used in marching bands. This trick can be performed regardless of whether you use a traditional or matched grip. Usually, the back stick is performed on the third or fourth beat in a measure.
There are two different ways to spin a drumstick. One is to hold the stick between your index and middle fingers and spin it, mainly by wobbling your wrist. This way is commonly referred to as a fake drumstick twirl; but even though it's referred to as "fake," it still looks impressive. The other twirling method involves spinning the stick between your fingers, like you might do with a pen. This trick is significantly harder to perfect, and may not be as practical to perform while marching.
This trick is done using the traditional grip. Start by hitting the drum normally then slip the stick between your pinkie and ring finger and roll your wrist over to hit the drum again. Make sure you don't hit the drum with the butt of the stick. Every hit should be done with the drumstick head.
Three-way back sticking is a more complicated variation of back sticking, and is also one of the most impressive tricks. The trick consists of three hits. The first hit is done normally. The second is a regular back stick, and the third requires you to swing your thumb under the stick and bring it down.