How can a defendant challenge the admissibilty of a piece of evidence?

A defendant can challenge the admissibility of evidence by filing a pre-trial motion to suppress, arguing that the evidence was obtained in violation of their rights, such as through unlawful search and seizure. They may also contest the relevance, reliability, or authenticity of the evidence during the trial. Additionally, the defendant can question the qualifications of expert witnesses or the methodology used to obtain scientific evidence. Ultimately, the judge will decide whether the evidence meets legal standards for admissibility.