Offside at a scrum occurs when players position themselves ahead of the hindmost foot of their teammate in open play. This offside line extends from the hindmost foot of the last player in the scrum, meaning that players must remain behind this line until the ball is out of the scrum. Offside infractions result in penalties or free kicks awarded to the non-offending team, providing them with an opportunity to gain territory or maintain possession. Teams must adhere to offside boundaries to ensure fair and continuous gameplay.