Though it mirrors the physical appearance of a fanny pack, the gear around the football player’s waist is far from it. If you’re unaware, the so-called fanny pack is actually a hand warmer; they play a vital role in football, especially in colder conditions.
Whether you’re watching a Pop Warner level game or a high-stakes professional matchup, plenty of football players don a hand warmer because obviously, you want to keep your hands from freezing off mid-game.
Source: https://www.distractify.com/p/why-do-football-players-wear-fanny-packs