Lag is a misunderstood concept. When powerful ball-strikers such as John Daly and then Sergio Garcia came onto the scene, and people could really see how much the clubhead trailed their hands as they were about halfway through the downswing, it became the goal of many golfers to try to create and maintain more lag. They figured all they had to do was hold off the release of the wrist angle they created at the top of the swing as long as possible--just like Daly and Garcia.
Well, here's the problem with swinging like this: If you don't let the clubhead release naturally, you're going to hit a lot of weak slices. The clubface will come into the ball too open, and you won't transfer enough energy into the hit. For good players, clubhead lag doesn't come from holding off the release. It's a product of the change of direction at the top of the swing. If you had a slow-motion camera, you would see Sergio's lower body moving toward the target and unwinding while the club is still completing the backswing.
So instead of thinking about "holding on" to your lag, focus on unhinging your wrists during the downswing so your arms are nearly straight at impact. Your wrists should be square to your target when the club meets the ball. You'll notice that your left forearm naturally rotates to do this (above, right). If you don't have any forearm rotation, then you're still trying to hold on too much.
Sean Foley, a Golf Digest Teaching Professional, is based at the Core Golf Junior Academy, outside of Orlando.