In American football, a guard is a player that lines up between the center and the tackles on the offensive line of a football team.
The guard's job is to protect the quarterback from the incoming defensive line and linebackers during pass plays, as well as creating openings (holes) for the running backs to head through. Guards perform speed blocking and "pulling"—sprinting out in front of a running back in order to block for him. Guards are automatically considered ineligible receivers, so they cannot intentionally touch a forward pass, unless it is to recover a fumble or is first touched by a defender or eligible receiver.
Right guards (RG) is the term for the guards on the right of the offensive line, while left guards (LG) are on the left.