P.R. Laws Ap. tit. 32A, § IV, Rule 45
(A) The credibility of a witness may be attacked or supported by evidence in the form of opinion or reputation, but subject to these limitations:
(1) The evidence may refer only to character for truthfulness or untruthfulness.
(2) Evidence of truthful character is admissible only after the character of the witness for truthfulness has been attacked by opinion or reputation evidence or otherwise.
(B) When attacking or supporting the credibility of a witness, only evidence as to specific conduct shall be admitted whenever it refers directly to the truthfulness or untruthfulness of the witness whose credibility is under consideration. The court may reject this kind of evidence whenever it determines that its probative value as to credibility has been overcome by other considerations, specially when challenging the truthfulness of a defendant in a criminal case. Nothing in this paragraph affects the admissibility of evidence of conviction of crime covered by Rule 46.