Seeking wording for a USASB scenario

[Tru_in_Blu]

I've been looking for actual wording for USASB that "protects" a player attempting to catch a popup on the infield.

Three players converged on a popup in the triangle among F1, F4, and F6. A runner on second base bumped F6 as F6 was tracking the ball INT was not called and F4 made a failed attempt to catch the ball. Runner returned to 2B and BR safe at 1B.

Defense wanted INT call on the runner at 2B. PU said that F4 was the primary player making a play on the batted ball.

I agree with the call but cannot find specific wording to that effect. Is there any?