Can outsiders be entrapped with castings of magic circle when they are currently being engaged on the battlefield?
Wow, this got buried in 40 minutes. Lots of activity on the ol' boards today.
From the spell text
"When focused inward, the spell binds a non-good called creature(such as those called by the lesser planar binding, planar binding, and greater planar binding spells) for a maximum of 24 hours per caster level, provided that you cast the spell that calls the creature within 1 round of casting the magic circle." (bolding the important bits)
So, no, you cannot. It must specifically be a called creature and it only works if cast within one round of a calling YOU initiated.
Thanks for the feedback. Had this come up in a game recently. People get the impression that you can use this spell as a touch attack.