 He did live in the Chicago area during his early boxing career before moving to Manhattan where the boxing was more lucrative, and there were still plenty of Irish fans who would flock to see who they assumed was a native son.Between May 1913 through May 1916 Brennan started professional boxing primarily in the New York area.With a powerful punch, he won an impressive 11 of his first fifteen fights by knockout losing only once in his first bout in Wisconsin.