First and foremost the best defense to any criminal allegation is that the defendant does not have to play offense. There is a presumption that the defendant is innocent, and the jury will be instructed on the presumption of innocence. The judge also admonishes the jury prior to trial that they are not allowed to use the defendant’s election not to testify as evidence of his or her guilt. Having said that, the defendant does have the same subpoena power as the State. The defendant is absolutely entitled to call his or her own witnesses, and have their lawyer cross examine all the witnesses that the State calls to testify against him.
Also, the State has the burden of proof in a criminal trial. The State must prove all the allegations in the charging instrument (indictment or information) beyond a reasonable doubt.
However, there are also defenses listed in the Texas Penal Code as well as justifications for committing criminal offenses where the conduct is excusable. For example, the most fundamental of these defenses is the right of self defense. Likewise, if you are defending another who is being attacked and it forces you to assault their assailant you have a defense. Also, if a fight is consented to there is the defense of mutual combat.
There are also justifications, such as necessity whereby the defendant is entitled to have the jury instructed that if his conduct was illegal and admitted to and there was a factual issue raised which might indicate that it was done out of necessity then they are made aware that they can find him not guilty.