Answer:

 

9 + 2 = 11
14 – 4 = 10
27 + 6 = 33
28 – 8 = 20

To get the score in the right column, points are added or subtracted to the numbers in the left column.
The number being added or subtracted (going from top to bottom) increases by two each time and alternates adding to the points or subtracting from the points.