【1】…is playing a role of a goalkeeper,which is seen as a giant from the offensive player's view, on the huge contrary, but from his own imagination as a dwarf.

【2】is playing a role of a goalkeeper,which is seen as a giant from the offensive player's view, on the huge contrary, but(which is seen) from his own imagination as a dwarf.

备注(1)：第1句可以理解为第2句省略了“主语(which)+谓语动词(is seen)”

备注(2):以上两个as的介词短语是作“主语补足语”成分，不是作宾语补足语成分。介词短语“as a giant”和介词短语“as a dwarf”

备注(3):以上两个from介词短语作状语成分。介词短语“from the offensive player's view” 和介词短语“from his own imagination”

备注(4):but为表示转折关系并列连词，意思“但是” 不可以公用，但可以理解为省略了“which is seen".连词but表示前面和后面是一种转折/对比关系。