Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
instīgātus, ūs, m. [instigo], an instigation, setting on: si instigatu alterius fera damnum dederit, Dig. 9, 1, 1, § 6.
instīgo, āvi, ātum, 1, v. a. [from in and stigo (unused), cf. Gr. στίζω; Sanscr. tig, tij, to be sharp; cf. stimulus for stig-mulus, stilus for stig-lus], to urge, stimulate, stir up, set on, incite, instigate (class.): si hic non insanit satis sua sponte, instiga, Ter. And. 4, 2, 9: instigante te, at your instigation, Cic. Pis. 11: cuncti sequentem Instigant studiis, stimulate him in the pursuit, Verg. A. 5, 228; 11, 730: Romanos in Hannibalem, Liv. 33, 47: comites agmen instigant, Ov. M. 3, 243: in arma, to rouse to arms, Vell. 1, 12: canem in aliquem, to set on one, Petr. 95: iracundiam, Sen. Ep. 10.
With inf.: laedere, Lucr. 4, 1082.