An animal like this don't need no 'pack' to get the drop on a friggen boxer.
Ghost, you're right that he'd likely win by mere size advantage, assuming the Boxer didn't get hold quickly. My contention is that a wild canine will withdraw from the conflict if he's taking any degree of serious bite damage, since willingness to do otherwise would be "bred" out of them by natural selection, i.e., those that did remain in the fight despite taking damage from a bite would end up lame, unable to hunt, and starve to death, thus not passing on that tendency.
With certain breeds of dog, it's just the opposite. Human selection has concentrated in certain breeds a high degree of disregard for personal injury and a determination to hold on a bite. There's a good chance IMO that this would freak a wolf out, if a Boxer (or other gripping type breed) were able to secure a grip early on, size disparity notwithstanding.
