Simply put, this is about comparatively small "good" characters or things being crushed underfoot by comparatively gigantic dangers. This can take two main forms.
First, a "straight" one, commonplace in cartoons involving mice, Incredible Shrinking Man scenarios, or normal-size humans who have to deal with Attack of the 50-Foot Whatever — but usually that's more a desperate attempt to avoid being trampled. Often associated with an Implacable Man or The Juggernaut.
Then, secondly, it can be used as a small Kick the Dog moment for a character so mean, evil or determined that nothing stands in their way; and just to prove it to the audience, the camera will turn to a shot of their feet (or their mount's feet), as they walk over and stomp on, crush or trample underfoot things that symbolize innocence, peace, happiness, or niceness, such as:
A flower or flowers
A doll
A small, cute woodland animal
Someone's body (or skull)
Fragile wedding china
Framed photo with breakable glass
Compare Giant Foot of Stomping and Fearsome Foot. Can be considered a Sub-Trope of Cruelty by Feet. Named after (but has absolutely nothing to do with) a song by Led Zeppelin. Not related to Curb-Stomp Battle, although a particularly brutal one-sided fight may involve actual stomping. If the villain intentionally uses their foot to trample an object of sentimental value to a character, that's Crush the Keepsake.
