Cut as shown on the first picture, then scoop out watermelon flesh (you can either use melon baller or just slice with knife or even a spoon (melon baller gives nice round shape tho!), as shown on the second picture.

Then make a zig zag cut on side to create a basket effect as picture number 3.

Place watermelon balls into basket and chill until ready to serve, covered in plastic cling wrap (you can also place some ice cubes before placing watermelon balls).