Dead Ball Foul

[Adam]

Originally Posted by Nevadaref

I started to think about B1 being still inbounds after retrieving the ball versus having obtained it and already moved OOB for the throw-in.

Despite the rule change for this season, I'd only call a foul in this case if the thrower was out-of-bounds, and then I would call an intentional personal foul.

The reason is that I would consider the ball to still be dead and not have started my throw-in count until B1 got OOB, thus the contact described would be ignored by rule, if it occurred during this dead-ball period following the goal. I wouldn't consider the action to warrant an intentional or flagrant contact technical based upon what the OP wrote.
However, once the ball is live that personal foul contact must be called and by rule must be deemed an intentional personal foul.

Since the OP stated "as he is beginning to throw the ball back in," I assumed B1 was OOB and the ball was live.

I tentatively agree with your final sentence. While Camron makes a good point, I think the point of the rule is to give the thrower an unfettered throw. Whether the player is legally OOB only means you don't add a DOG warning to the mix, IMO.