Everything happened pretty fast. They tried and failed to open the door, Ms. Asuka made it clear force wouldn't work, the Doctor tried some form of trickery but failed. Robin didn't entirely agree with the Doctor's hypothesis but it was certainly possible. "But why have us all out fight in this peaceful field? Given that this likely some form of entertainment and I'd bet we have an audience somewhere one would think atmosphere would be key. It doesn't make much sense...." Truthfully the tactician was just denying what was, in all probability the correct answer. So far he liked these people and really didn't want to hurt them. 

Though he'd already given a cursory tactical analysis of them all. Asuka seemed to be a very accomplished martial artist, that would be difficult. The Doctor didn't seem that threatening, though he apparently had some martial prowess given his stance earlier, not to mention he, like Robin, seemed more of the intellectual type meaning it was a good guess he'd have some form of tome or something on him. but Viridian....There's no telling what he could do. He could very easily possess some form of hex magic that could turn Robin into a frog. No best ere on the side of caution and avoid fighting until he had a better read.

It was then that the Doctor called out to another newcomer, a man garbed entirely in green standing atop the hill. And then the door opened, quite loudly. The Doctor seemed baffled which was odd. To Robin it couldn't have been more obvious. "It seems that the green man's presence opened the door. After all that is the only condition that has changed. Unless of course someone has fallen that we cannot see."