Gary Eugene Silas was convicted of aggravated assault and possession of a knife during the commission of a crime. Silas appeals, arguing that the evidence was insufficient to support his conviction. We affirm.

On appeal from a criminal conviction, the evidence is viewed in the light most favorable to the verdict. Paul v. State, 231 Ga. App. 528 (499 SE2d 914) (1998). We do not weigh the evidence or determine witness credibility but only determine whether the evidence is sufficient under Jackson v. Virginia, 443 U. S. 307 (99 SC 2781, 61 LE2d 560) (1979). The verdict must be upheld if any rational trier of fact could have found the essential elements of the crime beyond a reasonable doubt. Williams v. State, 233 Ga. App. 217 (1) (504 SE2d 53) (1998).

On appeal, Silas contends that he acted in self-defense, and that no rational trier of fact could have concluded otherwise based on the evidence presented. We disagree.

OCGA 16-3-21 (a) provides that: "[a] person is justified in threatening or using force against another when and to the extent that he reasonably believes that such threat or force is necessary to defend himself or a third person against such other's imminent use of unlawful force. . . ." It is well settled that once evidence of self-defense is presented, the burden is on the state to disprove that defense beyond a reasonable doubt. Hamilton v. State, 243 Ga. App. 10, 11 (532 SE2d 118) (2000); Manning v. State, 231 Ga. App. 584, 585 (3) (499 SE2d 650) (1998).

In the case sub judice, the defendant presented evidence that he acted in self-defense; however, the state rebutted this with evidence that he acted without justification. Significantly, the defendant's wife, Melissa Silas, testified that Bailey struck the first blow, and that her husband was merely defending himself; however, she was impeached by her prior sworn statement that: "[Gary Silas] and some guys was arguing and Gary pulled out a knife and cut the sixteen year old boy for no reason." While Bailey opined that "I believe [Silas] kind of felt that we probably was gonna jump on em [sic] cause I had Courtney and Quan walking behind me," there was substantial evidence that Silas attacked the teenager. All three of the young men testified that they were unarmed, that Silas was the aggressor, and that they did not strike Silas at any time during the incident.

"Witness credibility is to be determined by the jury, as is the question of self-defense when there is conflicting evidence on the issue." Hamilton, supra, citing Russell v. State, 267 Ga. 865, 866 (1) (485 SE2d 717) (1997). See also Strange v. State, 244 Ga. App. 635, 637 (1) (535 SE2d 315) (2000). The jury was free to accept or reject witness testimony that Silas acted in self-defense. See Knight v. State, 271 Ga. 557, 559 (1) (521 SE2d 819) (1999).