Not that I'm condoning his actions, but the short time I poped into the AvA not long ago, there were 12+ allies chasing one lone, wounded, bf110c. All of them had alt on him, and the entire freaking sector was littered with dots all chasing this one guy. I upped to try and help but there was just me vs 5 of them -- you do the math, I got cherry picked before I could get any one of them within 600d of my nose.
Maybe it's not poor sportsmanship if both sides do similar things? Maybe it's being fostered by the way the allies are flying?
Again, not that I condone these actions, they're deplorable. They might be explainable, however.