Parsing inflected forms may not always work as expected. If the following does not give the correct word, try Latin Words or Perseus.
concursātor, ōris, m. [concurso], one who runs hither and thither; in milit. lang., a skirmisher (opp. statarius; rare, perh. only in Livy): concursator et vagus pedes, Liv. 31, 35, 6: levis et concursator hostis, id. 27, 18, 14.