Mostly they were led by individuals with a penchant for political maneuvering and the factions were the instruments of their wielding of power. These were not typically actual participants in the sport. However there are a few examples of chariot drivers becoming initiators in a fracas. Once such was a driver in the 6th century called Porphyrius, who was supposedly born in Africa (Libya), but was reared in Constantinople, where he began racing with the Blue faction while still very young but then changed to the Greens under the emperor Anastasius and back to the Blues under Justin I.
He continued to race even into his sixties and seems to have adopted Calliopas as his name later in life. As the epigrams proclaim, he was the first charioteer to have his statues erected in the Hippodrome while still competing and the first to have a statue (indeed, at least two) from each faction. Malalas records for the year AD 507 that Kalliopas (Calliopas, the name by which Porphyrius is addressed in five of the epigrams), "an ex-factionarius [the most senior charioteer who drove for either the Blues or Greens] from Constantinople....took over the stable of the Green faction, which was vacant, and was completely victorious".
The interesting thing from our point of view is that like an early version of Beckham he toured the known world exercising his charioteering skills and even led an attack on the Jewish synagogue in Antioch in AD 507. "They set fire to it, plundered everything that was in the synagogue and massacred many people," setting up a cross there and turning the site into a martyrium (Chronicle, XVI.6). Whether this was on instructions from a higher power or not is not recorded.
However, Porphyrius was clearly partisan to the "powers that were" for in a fragment, Malalas also relates that Porphyrius helped rally support for the Emperor Anastasius during the revolt of Vitalian in AD 515 (cf. Epigram 350, where the emperor, "with the Greens to assist him, warred with the furiously raging enemy of the throne"). In appreciation, Anastasius, who, himself, favored the Reds, restored the privileges of the Greens and permitted them to erect a new statue of Porphyrius.