it is possible that you’ve somehow made some muscles very tight in the butt and this could be hitting on some nerves there sending pain down to your knee.  it may be that your standing on one leg may have done this, it may be something else in your form as kaitlin says.  i’d focus on first removing pain – it could mean you should see a PT – and relaxing those tight muscles.  Take some time off, smash gently not so vigorously in the first few sessions to let the muscles relax and return to normal, instead of hitting them hard in workouts and with a massage ball.