A definitive answer - sort of

[tharbert]

I think the key to the technical foul in JR's post is "intentionally" leaving the court to avoid a violation or a screen.

The defender with his foot OOB must be standing somewhere. It's not a violation for him to step on the line. Stepping OOB doesn't change his status as a player. I would call PC on A1 even though B1 clearly had a foot on the line.