Shoving

Grappling

https://roll20.net/compendium/dnd5e/Combat#content

https://olddungeonmaster.com/2016/12/13/dd-5e-the-attack-action/

A melee attack can be non-lethal...

https://rpg.stackexchange.com/questions/60066/how-does-knocked-out-work-in-5e

https://crobi.github.io/dnd5e-quickref/preview/quickref.html

How do I knock someone prone? What is Shove?

http://dnd5e.wikidot.com/feat:shield-master

Someone who takes the Shield Master feat can use their bonus action to make a Shove:

Shield Master
If you take the Attack action on your turn, you can use a bonus action to try to shove a creature within 5 feet of you with your shield.