The word is built from off and side, and a useful way to hold it is: not this side — the other one, the one away from where you belong. Stand on the pavement beside a car and one side is close to you; the far side, facing the moving traffic, is the off side. Carry the same picture onto a pitch. The rules give each player a side of the line they may be on, and a player who has drifted past it is on the wrong side of it — off side. In both pictures nothing has happened yet. The word only tells you where something is.
From the word’s history
From off plus side; compare German abseits, meaning out of the way or aside, and Dutch afzijdig.
來自 off 加 side。德文的 abseits（在一旁、離開路線）和荷蘭文的 afzijdig 都是同一種組合方式，都指「偏到旁邊去的那一側」。
Wiktionary entry for offside (kaikki:3f6f69a190036ae4:676781456:16981), supplied in the evidence packet
登入就可以看每一支怎麼連回核心畫面。