Leyline of Sanctity gives you hexproof, which prevents you from being targeted by spells and abilities that are controlled by an opponent. There are two ways that planeswalkers can receive damage; combat damage after they have specifically been attacked and by having damage from spells that would damage their controller redirected to a planeswalker they control. Leyline of Sanctity will not prevent a planeswalker from receiving combat damage, but it will prevent some spells from targeting the controller of a planeswalker.
For example, a player with Leyline of Sanctity cannot be targeted by a Fireball, so this Fireball will not be able to affect a planeswlkaer this person controls. However, spells that damage without targeting a player will get around the Leyline, and this damage can be redirected to a planeswalker. Chandra’s Outrage targets a creature and not a player. When one resolves, the controller of the Outrage can choose to redirect the two points of damage that would be dealt to the player to a planeswalker they control instead. A Leyline of Sanctity will not prevent this.
Today’s Rules Tip was suggested by Steve Peterman, a level 1 judge from Minneapolis, Minnesota, United States.