LogFAQs > #962083685

That's the idea. I think it could maybe refuse to leave the ball under those circumstances.

One last thing to note is that in at least one episode its been shown that Pokemon can refuse to leave their Pokeballs. The one episode I know this happens in is Dig those Diglett (it might have happened in others, but I can't think of any off the top of my head). In this episode several Pokemon refused to leave their balls and battle because they didn't want to fight a group of wild Diglett. And I don't mean one or two, I mean literally every trainer's Pokemon refused to fight. Now admittedly, I'm not sure if this happened in other episodes, season 1 in general had a lot of early installment weirdness, and the episode had its own... questionable moments. So take that as you will.