Propensity, or character, is admissible if character is an essential element of a claim, charge, or defense.

United States v. Munoz-Franco, 487 F.3d 25, 38-39 (1st Cir. 2007) (holding that "the Confrontation Clause present[ed] no bar to reliance on the absence of certain information from the Board meeting minutes to....The right of confrontation guaranteed by the Sixth Amendment to the Constitution of the United States bars the introduction against a criminal defendant of testimonial hearsay by a nontestifying declarant unless (i) the absent declarant is unavailable to testify at trial and (ii) the defendant had an adequate opportunity to cross-examine the absent declarant prior to trial.

United States v. Bradley, 390 F.3d 145, 154-155 (1st Cir. 2004) (upholding trial court's admission into evidence of accused's prior abusive treatment of other workers because "the intimidation of [the other workers] was part of a pattern of intimidation that carried over to [the complaining workers].").Other wrongs or crimes that show an unusual pattern of conduct by a person are not barred by the prohibition against the use of character or disposition to show conduct on a particular occasion.

Kanida v. Gulf Coast Medical Personnel, LP, 363 F.3d 568, 582 (5th Cir. 2004) (holding, in employee's action against employer for retaliation under Fair Labor Standards Act, that testimony of co-worker on employer's reaction to plaintiff's claim for overtime compensation was inadmissible character...The prohibition against circumstantial use of character -- the use of character or disposition to show conduct on a particular occasion -- applies in trials of civil actions.