You said: "Boat A (leeward) (both starboard) meets boat B near the starting line."
Then you said: "Boat B forces boat A down the line..."
Forget the racing rules, this is a violation of sailing rules/ROTR. Leeward boat (A) is privileged vessel, Boat B is the stand-on vessel.
If I were on Boat A, I would have called leeward, and requested that Boat B come up.
Also, even though Boat B is "in sequence" and therefore racing, if I were Boat B, I don't think I would have been such a jerk as to impede Boat A's late start.