Python

Check out Xnconvert, it’s completely free and was made for things like this. You can do a bunch of different actions on a set of images and specify where and how to save the output files.

@Shady_Shiroe

Open GIMP
Go to "File" > "Open" and select your GIF.
Select the "Crop Tool" from the toolbox.
Adjust the crop area to your desired size.
Click the "Crop" button.
Go to "File" > "Export As" and choose GIF as the format. Save your cropped GIF.

FFmpeg
Use the following command to crop the GIF, replacing input.gif with your GIF's filename and specifying the crop dimensions:

ffmpeg -i input.gif -vf "crop=w:h:x:y" output.gif

As far as i know, for pillow to do what you want you would need to

• Take a gif and split it in to frames
• Edit each frame individually
• Put frames back together as a gif
• Repeat for every gif
  
  It can be done automagically like you want, but if you're not interested in learning python maybe the XnConvert or ffmpeg comment above might be the way to go for ease of use.

As others have suggested, ffmpeg is a great cli tool. If you aren't comfortable with the terminal you can do it via python like this:

import os
import sys
import subprocess


def crop_media(file_name: str, w: int, h: int, x: int, y: int, new_dir: str) -> None:
    try:
        subprocess.run(f'ffmpeg -i "{file_name}" -vf "crop={w}:{h}:{x}:{y}" temp.gif -y',
                           shell=True, check=True, stdout=subprocess.DEVNULL, stderr=subprocess.DEVNULL)
        os.rename('temp.gif', os.path.join(new_dir, file_name))
    # Print the error and continue with other gifs, remove try block if you want a complete stop
    except subprocess.CalledProcessError as e:
        print(e)
    except KeyboardInterrupt:
        print('KeyboardInterrupt, cleaning up files...')
        os.remove('temp.gif')
        sys.exit(0)


def crop_directory(directory: str, w: int, h: int, x: int, y: int, new_dir: str) -> None:
    for root, _, files in directory:
        for file in files:
            if not file.endswith('.gif'):
                continue
            if os.path.isfile(os.path.join(new_dir, file)):
                print(f'{file} already exists in {new_dir}, skipping...')
                continue

            file_path = os.path.normpath(os.path.join(root, file))
            crop_media(file_path, w, h, x, y, new_dir)


if __name__ == '__main__':
    width = 0
    height = 0
    x_offset = 0
    y_offset = 0
    gif_directory = ''
    new_directory = ''
    crop_directory(gif_directory, width, height, x_offset, y_offset, new_directory)

This should go through every file in the directory and subdirectories and call the ffmpeg command on each .gif. With new_directory you can set a directory to store every cropped .gif. The ffmpeg command is based on johnpiers suggestion.

The script assumes unique filenames for each gif and should work with spaces in the filenames. If they aren't unique, you can just remove the new_directory part, but you will then lose the original gif that you cropped.