You can think of a spotter as a borrowed pair of eyes. Someone is put where they can see what the people in the middle of the action cannot — the whole field, the blind side of a truck, the bar above a lifter's face, the one bird in the tree. Whatever happens next, their part is to see it first and say so.
spotter 可以想成「借給別人的一雙眼睛」。有人被放在一個看得到全場的位置。場上的人、開車的人、正在舉重的人，都有自己看不到的地方。這個人就負責幫他們看。看到了，就講出來、記下來，或者伸手接住。不管接下來要做什麼，他的價值都在「先看見」這一步。
From the word’s history
From spot + -er. As a verb, spot means to see and recognise something, so a spotter is simply the one who does the seeing.
這個字來自 spot 加上 -er。spot 當動詞是「看見並認出來」，-er 是「做這件事的人」。所以 spotter 字面上就是「負責看出來的那個人」，而它每一個用法都還守著這件事。
Wiktionary, "spotter"
登入就可以看每一支怎麼連回核心畫面。