Tex. Civil Practice and Remedies Code § 11.054

A court may find a plaintiff a vexatious litigant if the defendant shows that there is not a reasonable probability that the plaintiff will prevail in the litigation against the defendant and that:

(1) the plaintiff, in the seven-year period immediately preceding the date the defendant makes the motion under Section 11.051, has commenced, prosecuted, or maintained at least five litigations as a pro se litigant other than in a small claims court that have been:

(A) finally determined adversely to the plaintiff;

(B) permitted to remain pending at least two years without having been brought to trial or hearing; or

(C) determined by a trial or appellate court to be frivolous or groundless under state or federal laws or rules of procedure;

(2) after a litigation has been finally determined against the plaintiff, the plaintiff repeatedly relitigates or attempts to relitigate, pro se, either:

(A) the validity of the determination against the same defendant as to whom the litigation was finally determined; or

(B) the cause of action, claim, controversy, or any of the issues of fact or law determined or concluded by the final determination against the same defendant as to whom the litigation was finally determined; or

(3) the plaintiff has previously been declared to be a vexatious litigant by a state or federal court in an action or proceeding based on the same or substantially similar facts, transition, or occurrence.