Doesn't matter. It was an accident, but you still are liable for a dog breaking free of it's leash. As an owner, you are responsible at all times for controlling your dog. Just because you tried to control the dog and failed doesn't excuse you of liability. I see too many people who cannot control their dogs, or do not have them properly leashed. This is an accident which should be prevented by proper training/leashing. Both parties are at fault, and both are irresponsible dog owners. The poodle owner doesn't have a leg to stand on as he/she allowed it to roam, and the boxer's owner had no control over an aggressive and powerful dog. This is the unfortunate truth. If everyone took their responsibilities as dog owners as seriously as you do, it would be much easier. You wouldn't be at fault if your leashed dog attacked a loose dog approaching it, but why should you be put in that position?