Thing is, anything that will knock a human down will also do much more. There is no nice setting between “lethal” and “non lethal” weapons. A strong push of air will knock somebody down. And rupture their eardrums, and maybe break a rib puncturing their lungs and kill them. Or just explode an eyeball if the blasts hits the wrong way. Or they just suffocate because the shock collapses their lungs.
We can easily knock people down. The problem is, they usually never get up afterwards.
Well, there are lasers.
https://en.wikipedia.org/wiki/HELIOS
The High Energy Laser with Integrated Optical-dazzler and Surveillance (HELIOS) or Mk 5 Mod 0 HELIOS[1] is a Lockheed Martin-developed 60 kilowatt high-energy laser weapon designed to intercept combat drones, fast-attack craft, and missiles.[2] After winning the contract in 2018, the first announced installation was on USS Preble (DDG-88) in 2019.[3] By 2021, it was reportedly deployed onto the Arleigh Burke-class ship as part of its anti-air Aegis Combat System.[2][4]
Lasers don’t exert force, though. Just heat.
(Ok, technically that’s not true. Light does exert force, but it produces so much more heat than force that even lasers many many orders of magnitude weaker would simply vaporize just about anything they hit.)
The vaporized surface material can actually produce a lot of force
Soundwaves can be powerful enough to deafen, disorient, knock over, or even kill.
Directing sound potent enough to do this from more than a few few, tho, is kinda hard but they have seen use as anti-riot devices.
Anything harder than air will turn you into a sludge on the pavement. Even water will rip your skin off and break bones.
