How do I get the big points?
Form lines longer than 5 by leaving a "gap" in the middle of the line that you fill in later (or runs in another direction)
What's the largest number of balls that can be formed?
With a perfect layout (an X overlayed on a +, with one of the "arms" of the + missing, filling in the middle with the last ball), you can, in theory, remove 7 x 4 + 1 = 29 balls in one swoop.