Capítulo 174: Courageous Clash With Fire Dragon

But, the Azure Attire Force field barrier activated and Seth was well protected right as the fire dragon clasped its maw, he was shot back like a volleyball, and the dragon too flew back and smashed at the canyon wall, creating a deep crater.

Force field barrier has the effect of repelling all physical attacks. Crodo was repelled, Dave was repelled and Chief Yellow Monster was repelled but Seth was never repelled until now. However, even though Seth was repelled, the force on Fire Dragon was stronger than Seth's. 

The reason was that the dragon was truly a higher life form than Seth and thus rules must alter a bit. If Seth was facing Young Dragon, Seth will be the only one repelled and the young dragon will just stone for a moment.

Also, if he was facing an Adult Dragon, and it was serious, the force field would just be a momentary nuisance.