The Rattay tourney is held once a week (as far as I can tell) at the upper castle in Rattay. It's all for leveling your stats through combat and mastering combat controls.
DO NOT EVEN ATTEMPT THIS UNTIL YOU DO ALL TRAINING WITH CAPTAIN BERNARD
For whatever reason, YOU ARE NOT ALLOWED to do any tricks like clinching UNTIL you learn it from Bernard. YOU ARE NOT ALLOWED to counter until you learn it from Bernard. They, however, are not Henry, and they can bash your head in with the hilt of their sword all they like, and you can't do anything about it. All of your combos outside of slash-stab-repeat are locked behind perk points.
IMO, combat is busted, so good luck with this one, especially if you've just started.
Something else that bugs me is that the enemy can send his shortsword straight for your eye (hits your chest/neck) over your shield and Henry doesn't instinctively raise his shield to stop it. You don't need training to cover your frickin eyes.