Well,... no. That's not barging. "Barging" refers to a boat that takes room at a starting mark when she isn't entitled to do so. Rule 18 (Rounding and Passing Marks and Obstructions) explictly turns off at "...a starting mark surrounded by navigable water..." so only rule 11 (On the Same Tack, Overlapped) applies. A windward boat can't stick her nose between a starting mark (a.k.a. committee boat or "barge") and a leeward boat. If she makes the leeward boat bear away, then she breaks rule 11 by "barging".

Regards,
Eric