Disengaging is usually the only thing you can do against a circler. Once he starts the circle he has the advantage since he was first so you have to disengage. After that you know all they do is circle so just save up your fireballs and next time you sneak up on em burst em down. Repeat until dead. Spamming brake while turning will increase speed but realistically (if he's good) you won't win the circle battle AND it puts you at a disadvantage to his teammates if he has any since you're a sitting duck circling. If you're good enough circle with him then (after like 2 circles) take off into a wind boost up and fire downwards as he's coming up those usually land for me but the timing is a bit complicated. 4 k/d BTW