This daily can be pretty tough if you don't know what you are doing. You have to challenge riders from your faction to a joust and it can get tough at sometimes..so here's the exploit:
Have a friend nearby DPS the rider you are facing. It's that simple. However you will need to keep breaking the shield because it DOES reduce damage from all sources (30/60/90%) if you don't break it. I hardly think this is intended, because you are not allowed to fight it while on your jousting mount. Each rider has about 50,000 HP, but any good DPS can whittle that down in no time.