I buy a case of lacrosse balls every once in awhile, and I have never even played lacrosse. Why? Because lacrosse balls are perfect for giving yourself a little soft-tissue work when you need it.
The pressure of a lacrosse ball works similarly to the hands of a masseuse--of course, less skilled, but in a pinch it is so much better than nothing. The relief you feel when someone gives you a good rub-down can be replicated yourself using a lacrosse ball.
I'm not gonna lie--it hurts! In fact, you may need to start with a tennis ball because it's less pressure. The problem with the tennis ball is that, especially for larger folks, it can deform to the point that it doesn't apply enough pressure.
There is no hard-and-fast rule on how to use the ball, but you want to place it under tense muscle tissue, roll back and fourth over the spot, and move the limbs around the area a bit. For example, if you have the ball on the side of your glute, and you are sitting on the ball, move your leg from your hip in and out as you apply the pressure. This movement helps loosen things up more efficiently.
Spend several minutes over each area you want to work. Apply as much pressure as you can stand!
You can also put two lacrosse balls in a sock for use up and down your spine and just below your neck.
It's supposed to hurt a little--that's how you know it's working. However, if you truly can't stand it, feel free to use a tennis ball instead.