A defendant can ask for another judge if he feels the judge has a bias or prejudice against him. Christensen v. State, 245 Ga. App. 165 (2000). This is called a motion to recuse the judge.
Recusal is required, under judicial ethical standards, whenever a trial judge's "impartiality might reasonably be questioned." Birt v. State, 256 Ga. 483 (1986); Uniform Superior Court Rule 25.1; Gude v. State, 289 Ga. 46 (2011). In order to be disqualifying, the alleged bias must come from an extrajudicial source and result in an opinion of the case based upon something other than what the judge learned from the case. Rooney v. State, 311 Ga. App. 376 (2011). Recusal cannot be based upon the judge's prior rulings in similar cases. Moore v. State, 313 Ga. App. 519 (2012). A motion to recuse must be supported by an affidavit. All motions to recuse or disqualify a judge in a particular case or proceeding shall be timely filed in writing and all evidence thereon shall be presented by accompanying affidavit(s) which shall state the facts upon which the motion is based. The filing and presentation of the affidavit to the judge shall be no later than five days after the affiant first learned of the alleged grounds for disqualification, and not later than ten days prior to the hearing or trial which is the subject of recusal or disqualification, unless good cause is shown for failure to meet such time requirements. In no event shall the motion be allowed to delay the trial or proceeding. Uniform Superior Court Rule 25.1; Hampton v. State, 289 Ga. 621 (2011).
The affidavit must clearly state the facts and reasons for the belief that bias or prejudice exists, being definite and specific as to time, place, persons and circumstances of extra judicial conduct or statements, which demonstrate either bias in favor of any adverse party, or prejudice toward the moving party in particular, or a systematic pattern of prejudicial conduct toward persons similarly situated to the moving party, which would influence the judge and impede or prevent impartiality in the defendant's case. Allegations consisting of bare conclusions and opinions shall not be legally sufficient to support the motion or require further proceedings Uniform Superior Court Rule 25.2
When a judge is presented with a motion to recuse, or disqualify, accompanied by an affidavit, the judge shall temporarily cease to act upon the merits of the case and shall immediately determine the timeliness of the motion and the legal sufficiency of the affidavit, and make a determination, assuming any of the facts alleged in the affidavit to be true, whether recusal would be warranted. Braddy v. State, 316 Ga. App. 292 (2012); Christensen v. State, 245 Ga. App. 165 (2000). If it is found that the motion is timely, that the affidavit is sufficient and that recusal would be authorized if some or all of the facts set forth in the affidavit are true, another judge shall be assigned to hear the motion to recuse. Uniform Superior Court Rule 25.3.