Hey Pelican,
Was your game settled before you noticed the side movement? In other terms, have you been playing for a long time with the same stance before noticing the unwanted movement?
I'm no doctor, but aging (and other changes in your body) may well cause you to suddenly develop a bad habit, even after years of playing. I myself recently lost 40 lbs and I had to revisit my entire stance, because I just couldn't play well anymore. You might have gotten stiff somewhere and your stance might have changed suddenly. I have noticed things like that often happen all of the sudden.
Now, about your side movement, what is it you notice exactly? If you notice your tip drifting from left to right as you stroke from back to front (or vice-versa) slowly and regularly, in pace with your stroke, I bet you anything you're slightly out of position, i.e. your shooting arm doesn't travel exactly in the elbow plane anymore. Assuming the way you address the ball and position yourself correctly already (which, not knowing you, isn't necessarily the case mind you), I would try one or more of the following changes:
- When you address the ball, increase or decrease slightly the angle between your feet and the cue, so your hip are more or less rotated,
- Try playing with your legs a little straigher or a little more bent. This changes the angle between your cue and your torso. Sometimes it places your rear shoulder in the right position,
- When you're down on the shot, try rotating your entire upper torso (shoulders) more or less, that is, "tuck in" more or less, *while maintaining a limp shooting forearm* and compensating for the lateral drift of your cue by moving your body, not twisting your shooting arm. This usually has the most dramatic effect on unwanted lateral cue movements during the stroke, so don't overdo it. However, be sure to try that with your shooting forearm LIMP, otherwise you'll develop a faulty stroke,
- If the lateral movement is very small, you may want to try rotating your shooting arm's wrist in or out slightly, while maintaining a loose grip and your wrist in line with your forearm. When you do that, you modify very slightly the pulling point of the biceps in the elbow joint, which might just correct a residual stroking defect.
You can play with those variables and see what they do to your stroke,
if you're certain your fundamentals are already good. When you change something, you'll know if your stroke improves or not, and you'll know where to go to recover a proper stroke. If something has changed in your body due to aging or anything else, you might be able to make a small change to your habits and correct your stroke that way.
But if you're unsure of your fundamentals, or if nothing you try works, I strongly suggest contacting an instructor who will help you with your position.
All the above is assuming you have a simple out-of-whack position. If however you notice jerky or random movements while you stroke, I would consult a doctor. If only your forearm moves during your stroke, it's a simple pendulum, and stroke defects should look smooth, regular and repeatable. If your defect is semi-random or not repeatable, especially if you played correctly before, you may want to do a checkup.
I hope this'll help. It's not easy to give advice without knowing you, so if you have any doubt, just call an instructor and you'll get the straight dope on your playing stance
