Hunting Experience.

The experience of others is something fourth is not lacking in. He may be young and hasn't seen much of the world, but he has a lot of experience gained from his predecessors. So he wasn't caught off guard when the three-tailed tunda pounced at him during his hunt. 

A translucent blur shot out from a shrub close to him and swiped a claw at him. His body leaned back at the last moment to dodge the attack. A paw with four white claws ripped the air in front of his face and passed by. His coiled muscles sprung into action after that.

His muscles were already coiled before the assault. Leaning back had compressed them further. So he simply let go of the contraction. They relaxed, and in so doing, they catapulted him forward. His neck and the head attached to it sprung forward like a spring, and his opened mouth latched onto the neck of the tunda.