From Sonic Retro
Fireball is Team Chaotix's variant of the Fire Dunk in Sonic Heroes. When in Power Formation with Vector as the leader, Team Chaotix can enter Fire Combination by pressing , which sees Espio and Charmy clenched in Vector's teeth as spin rolling spheres.
The Fireball attack sees Vector spit his teammates out as missiles at enemies by pressing . The attack can also be used to break down doors and other obstacles. Using it in the air is called Jump Fireball.