Dog A and and Owner A (DA & OA from here) are playing in the park off leash with several other dogs and their owners. All are getting along swimmingly. The pack is happy and stable. DA is the oldest of the pack, has raised a litter of puppies, and is the dominant member of the 4-legged pack.
Dog B and Owner B (DB and OB from here) enter the environment with DB on leash and stop to socialize.
DA is a 60-lb pooch.
DB is a 7-lb pooch.
The 4 established pack members approach DB to greet him by bowing their heads and attempting to sniff DB's backside.
After a few seconds, DB raises his lip, bears his teeth, and then quickly follows with a warning snap directed at DA.
DA retaliates vocally and physically by pinning DB.
OA grabs DA from behind, and in an instant, DA releases, retreats, and it's over. OA corrects DA and they are subsequently at approximately Level-2 intensity.
Meanwhile, OB has picked up DB, and begins to berate OA at approximately Level-8 and quickly walks away - still chastising OA in front of the other pack members and their stable owners. OA is deflated and embarrassed. OA pursues OB to verify that DB is unharmed. OB states that DA is an aggressive dog, should never be off leash, that DA attacked DB, and that it's not a fair "fight" because DB is only 7-lbs.
1) How would you characterize the demeanor of DA and DB?
2) What, in your opinion, was the trigger point?
3) What could have been done to avoid this - or more specifically, what is the desired behavior from: OA, OB, DA, DB?