[Dakota]

Can someone please show me where the rules say the fielder in possession of the ball must be actually making a play on the runner supposedly obstructed?

If the fielder has possession, there is no possibility of obstruction.

Fielder attempting to execute a double play: Bases loaded bottom of 7th tie score no outs situation. Priority of the defense is to prevent the score. Bunt fielded by F1. F1 has the ball but is attempting to throw out R1, and steps into the path of BR, causing BR to run wide. Throw to F2 is successful for the out, throw back to F4 covering 1st base is successful for the double play on a very close call. BR would likely have been safe had she not run wide to avoid F1. No obstruction here... F1 had the ball.

(Edited for clarity - see italicized words, above.)