Hi,
There are two ways to crop out the bottom 1/4 of a video clip.
The first way is to use the Crop to Fill option in the corp controls, and crop it in the timeline. That would remove the bottom 1/4, but also would remove material at the sides and top. So, for example, if you started with this clip. . .

, , ,and used the Crop to Fill option, you would get the clip below (with the foreground removed but also the building on the left is removed.

The second way is to crop the original video clip in the browser screen (above the timeline). The available crop controls are much more versatile and allow custom cropping. So, cropping in the browser screen would give you this look:

As you can see, the foreground is removed but the building on the left and the trees on the right remain. The aspect ratio is changed a bit to accommodate the crop of the lower 1/4.
Experiment for yourself and decide which method produces the effect that you want.
-- Rich