back four
noun [ S ] uk/ˌbæk ˈfɔːr/ us/ˌbæk ˈfɔːr/
（足球的）四卫式（通常由两名后卫和两名中卫组成的战术阵形）
on a football team, the two centre halfs and the two fullbacks, who together form the defence
Mulumbu plays just in front of the back four. 穆隆布在球场上的位置是在四后卫前一点的地方。