LBW confuses people because several checks happen one after another. If one check fails, the batter is not out, even if another part of the appeal looks strong.
LBW requires the ball to hit the striker's person without first touching the bat. A tiny inside edge before the pad therefore ends the LBW case, even if ball-tracking later predicts a direct hit on the stumps. Contact with the pad before the bat does not receive the same protection. On review, the third umpire normally settles this question with synchronized sound and pictures before moving to the location and projection checks.
Pitching describes where the ball first bounced. If any part of it pitched outside the line of leg stump, the striker cannot be out LBW. A ball pitching outside off stump remains eligible. Impact describes the later point where the ball hit the striker's person. Impact in line can qualify; impact outside leg does not. Impact outside off can qualify only when the striker made no genuine attempt to play the ball with the bat. A batter leaving, padding the ball away, or offering no stroke therefore gives the umpire a wider outside-off impact test, but it never removes the protection for a ball pitching outside leg.
Once the earlier conditions survive, the umpire imagines the path the ball would have followed after impact. Pace, swing, seam, spin, bounce, and the distance still to travel all affect whether it would have hit any part of the wicket. The question is not whether the ball looked straight at release, nor whether it struck the batter directly in front. A turning ball can hit a pad outside the crease and still miss; a ball angling across the batter can hit in line yet continue past the stumps. In DRS matches, ball-tracking assists this projection, with the competition's umpire's-call margins preserving close elements of the original decision.
The name says leg before wicket, but the Law refers more broadly to the striker's person. An eligible delivery can strike a knee, boot, torso, or another part of the body and still produce an LBW decision if every other condition is met. Height then becomes part of the projected-path question: contact high on the body often means the ball would have passed over the wicket, but the contact point alone is not an automatic verdict.
That is only one part of LBW. The ball can be hitting the stumps and still be not out if it pitched outside leg stump or hit the batter in the wrong place under the law.