Knockdown may refer to:
- "Knockdown" (song), a song by Alesha Dixon
- Knockdown, in full-contact combat sports, when a fighter is down or vulnerable, often preliminary to a knockout
- Knockdown, a fictional character in the Transformers universe, partnered with Swoop, Terrorsaur, and Nightscream
- Knockdown texture, a drywall finishing style
- Gene knockdown, a genetic modification technique
- Knockdown kit, a complete kit needed to assemble a vehicle
- Knockdown (G.I. Joe), a fictional character in the G.I. Joe universe
- knockdown, nautical terminology for a near-capsize where the boat self-rights