rearguard
/ˈrɪəgɑːd/noun
1- the soldiers positioned at the rear of a body of troops, especially those protecting an army when it is in retreat后卫, 后卫部队。
1.1
- a defensive or conservative element in an organization or community（组织或团体中的）防御（或保守）成分。
1.2
- (in team sports) a defending player or players（团队比赛用语）后卫。
词源
late Middle English (denoting the rear part of an army)： from Old French rereguarde.