Clarification about Back Court Violation

[Scrapper1]

Rule 12?

Team control was NOT lost, so your partner is correct about that. But it's only a violation if, during team control, Team A is the last to touch the ball before it goes in the backcourt and then is also the first to touch it after it goes into the backcourt.

Since the Team B defender is the last one to touch the ball before it went to the backcourt (by knocking it out of A1's hands), there is no penalty if A1 goes to retrieve it in the backcourt.