Sciatica is a common condition that, typically, produces pain across the buttocks on one side and down the back of the leg. Sometimes there is numbness and/or tingling in addition to the pain. It follows the line of the sciatic nerve, which is the largest nerve in the body. This nerve has to pass through or around several muscles in the pelvic cavity, one of which is the piriformis muscle. Sometimes it passes through the piriformis and sometimes underneath, and sometimes it splits and one part goes through and the other underneath. Either way the piriformis muscle can cause quite a lot of trouble for the sciatic nerve. The reason for this is that this muscle can and does go into spasm quite regularly, particularly in active people in general and sports people in particular.
The main function of the piriformis is to rotate the thigh outwards ( or laterally, as medics like to say), which is something we all do many, many times a day. When it goes into spasm it squeezes the sciatic nerve, which then lets you know about it in the form of pain. Even if it doesn't go through but underneath the piriformis it can still get squeezed between the pitiformis and the adjacent muscles. The solution is to get the piriformis to relax, thereby taking the pressure off the sciatic nerve. Or sometimes the whole area can be in spasm, so several muscles will need to be treated, but this is usually something that can be resolved in two or three treatments, which most people find a painless and relaxing experience.