As stated in the Official NHL (National Hockey League) Rulebook in rule 76.6, players must comply by the following standards, otherwise it will result in a face-off violation:
i) Encroachment by any player other than the center into the face-off
area prior to the puck being dropped.
ii) Encroachment by any player into the area between the hash marks on
the outer edges of the face-off circle prior to the puck being
dropped. Players must also ensure that both of their skates do not
cross their respective hash marks.
iii) Any physical contact with an opponent prior to the puck being
iv) Failure by either center taking the face-off to properly position
himself behind the restraining lines or place his stick on the ice (as
outlined in Rule 76.4).
v) The blade of the stick must then be placed on the ice (at least the
toe of the blade of the stick) within the designated face-off area.
Violation of these rules will result in removal from the face-off (the
center) and normally one of the wingers comes in to take the re-drop.
Any 2 face-off violations committed by the same team during the same
face-off will result in a Delay of Game minor penalty for 2 minutes.
Included is also a link to the Official Rulebook for further reading and long form rules: