There are some situations where arena battles can get stuck and go on ad infinitum. For example both teams are left with one champion each, one with an attacker with Lifesteal set and the other with an healer like Apothecary. Perhaps the attacker is spirit affinity and can't do enough damage to apotechary, but he can sustain himself with the lifesteal set. So no one of the heroes is going to die at any point and you're forced to leave the battle and lose and this is not fair.
This also mean that you can actually win arena defense battles without killing any of the other champions, for example let's say I have a team of 4 well equipped healers that don't do much dmg and are never going to kill an enemy, but they heal each other continuously and are never going to die... I don't think this is how you're supposed to win arena battles

Please find a way to get around this. What I was thinking was: if the battles takes more than 5 minuts (which generally means the battle is getting stuck) place a button that "resolve" the battle based on something like who did the most damage OR who has more champions left / more team power
EDIT: This solution could be exploited by players by not acting for 5 minutes and win the battle so it's probably not good enough and need something else to function properly