"Double tip" BC Violation

[jdw3018]

I've had it once this year...with an added element:

A1 makes an unsuccessful try from the baseline. Following is a scrum for the rebound with a loose ball batted around on the ground between players. A2 grabs the ball sitting on the court, attempts to pass to A3 beyond the top of the key. B1 tips the pass, which is subsequently tipped by A4, the ball then goes into the backcourt where A3 tracks it down. I called backcourt.

To the coach's credit (I was right in front of him at the time), he asked and then fully accepted the explanation. Seemed he knew the rule, which is rare indeed...