The Doctor's hand hovered over the coordinate settings. This one was trickier than it looked, actually. If he didn't give it long enough to allow the fifth planet's recorded sporting holy war history to happen, it would destabilise the entire temporal structure of coalition space. Probably. On the other hand, it seemed -- well, unsporting to let it run on too far in case they devastated the entire planet. Poisonous scrum gas and high explosive penalty spots were pretty nasty stuff.
He might have known it would be a bad idea to bring Rhys and Mickey here and let them do their own thing. Oh well ... call it a couple of hundred years. That should do it, near enough. He landed the TARDIS and paused before opening the doors. Come to think of it, how did you stop bitter warfare between the forces of the Church of the Blessed Rugby Sevens and the Hallowed Temple of Five-a-Side, and teach them a better way?
Wait a minute -- what about that stuff he'd shoved in store cupboard 574-C five regenerations ago, and never bothered with since?
Half an hour later the Doctor strolled out whistling into the middle of a battle-match, dressed in an old jumper he hadn't worn for decades, and carrying a kit bag full of objects made from leather and willow.