In section 1983 action alleging that defendants-police officers subjected plaintiff to false arrest and excessive force, plaintiff waived any issue regarding propriety of Dist. Ct.’s denial of his motion seeking to exclude from evidence seven of plaintiff’s criminal convictions that were entered within past 10 years, where plaintiff failed to properly develop in Dist. Ct. his contention on appeal that Dist. Ct. had failed under Rule 609 to articulate required probative-prejudice balancing test for each conviction. Fact that defendants addressed said balancing test in their opposition brief before Dist. Ct. did not serve to preserve issue for appellate review.