I'm not saying I want to limit you & take away your 'golden apples' and I do understand where you are coming from. What I am saying is that I don't agree with the idea of limiting the attacks to non-responsive players. I pick players off the battle list & attack till they are down & move on to the next. If I win, great.. If I don't win, I move on or look at why I'm losing & try to adjust various weapons, boosts etc so I can win. Sometimes it works, sometimes not.. but that's what I enjoy about the games, strategy. The other thing is everyone has their own definition of overkill. For some it's more than 2-3 attacks. Others its over 10. So it's hard to gage a general limit for everyone I'm sure. Personally, I don't have a number. If you are on the list, you're fair game till you're off the list & I expect to be treated the same way.
On the other hand, what could help is an updated in game message like the one Eddie suggested above. I would be respectful to someone who lets me know that are busy or trying to fight Bosses only & not able to battle one on one. The only thing I do see as an issue with this msg is some people would use it all the time to get out of fighting all together.