Hold one picture: a flat set of iron bars, laid side by side with even gaps between them, sitting over a fire. That is the cooking frame the word names first. Everything else this word does is that pattern seen somewhere else — the same even, parallel lines drawn on something much bigger. Once the pattern is in your eye, a marked football field and an old kitchen rack stop looking like two unrelated things.
From the word’s history
The dictionary traces gridiron to Middle English gridel, a griddle; the ending drifted until it sounded like iron, and the word was rewritten as if it were grid plus iron. The modern word grid was then pulled back out of it.
字典把 gridiron 追到中古英文的 gridel（烤盤）。字尾一路走音，最後被聽成 iron（鐵），整個字就被寫成好像是 grid 加 iron。更有意思的是，grid（格子）反而是後來從這個字拆出來的，所以「格子」這個概念在英文裡等於是從這面鐵架上長出來的。
Wiktionary entry for gridiron, packet source_ref kaikki:3f6f69a190036ae4:1224874039 — 'variants of Middle English gredire ... itself an alteration of Middle English gridel (griddle). The ending was assimilated to iron, as if from grid + iron, whence grid was later derived.'
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