osporiti

1. to dispute; to challenge; to contest
   Opozicija je osporila rezultate izbora. — The opposition challenged the election results.
   Niko ne može da ospori njegov talenat. — No one can deny his talent.
2. (someone + acc.) to deny someone's right
   Rođaci su mu osporili pravo na nasledstvo. — His relatives disputed his right to the inheritance.

The imperfective is osporavati; the person whose right is denied is in the dative.