[1][10] As a journalist, Hillmann has written for NPR as well as for publications including the Toronto Star, Playboy, Chicago Tribune, Salon, Daily Mail, Los Angeles Times, Stuff, and The Washington Post.

[33] He has given expert commentary on the running of the bulls for CNN,[34] The Today Show,[35] CBS This Morning,[36] BBC World Service,[37] and Esquire Network.

[39] He was inspired to join the tradition by Ernest Hemingway's book The Sun Also Rises,[40][41] and has taken part in the bull runs in Pamplona since 2005.

[43][44] By 2013 he had acquired the nickname "Buffalo Bill Hillmann", and in 2014 he co-authored the book Fiesta: How to Survive the Bulls of Pamplona with Alexander Fiske-Harrison and John Hemingway.

[45][46] On July 9, 2014, a bull named Bravito [47](Spanish for Brave one), gored Hillmann twice in the thigh at the festival of San Fermín in Pamplona,[45][46][48] but he returned to bull-running in Pamplona in 2015,[41] and published his memoir, Mozos: A Decade Running with the Bulls.