Short answer:

The name comes from the verb bleach — because the original open-air wooden spectator planks were sun‑bleached / faded pale by direct sunlight.

Full origin

1. It is an American English term, first recorded for baseball fields in the late 1800s (written as “bleaching boards” as early as 1877, then “bleachers” by 1889).

2. Early bleachers were simple, uncovered wooden tiered benches with no roof. Constant sunshine turned the raw wood pale, or “bleached.” So people called them bleachers.

3. A lesser folk story says it referred to fans getting sun‑bleached (tanned/burned) while sitting there, but the primary, dictionary‑accepted origin refers to the wooden planks, not the people.

Modern note

Today we still say bleachers even for indoor telescopic bleachers (like Yunxinda’s retractable gym stands) or aluminum/plastic models. The sun‑bleaching literal meaning is no longer relevant — it is just the standard North American word for this tiered spectator seating.

British English normally calls this kind of seating stands or tiered seating, not bleachers.