Runners are one thing, but the kids that forfeit because their opponent takes an early lead REALLY píss many people off. The ability to forfeit needs to be removed.
Either remove the "Return to Town" button or
Make the forfeiting player receive NOTHING. Remove two stars and grant NO AP. Credit the winner with three kills worth of AP and grant one star as normal.
As for the people who force quit the app. As suggested above, give the quitter NO AP, take two stars, and give the winning player credit for three kills and a single star.
To support this.. Imagine you spend gems entering the arena, only to have what would have been ~50 AP taken from you by some unskilled player just straight up quitting after you get the first hit, leaving you with no kills and a measly 16 AP. It really gets on the nerves of many.
We should not be penalized because our opponent decides to quit.