[1] Hallahan was a co-captain of the Dandenong Stingrays team in the TAC Cup in 2010, but an ankle injury during the season caused a drop-off in form.

[2] In 2012 and 2013, Hallahan played exclusively with Hawthorn's VFL-affiliate, Box Hill Hawks.

In 2013 he won the J.J. Liston Trophy in a three-way tie with Steve Clifton (North Ballarat) and Jordan Schroder (Geelong), all on 17 votes.

[3] Hallahan was selected to make his debut for Hawthorn against Geelong at the MCG on Easter Monday, 2014.

[4] On 16 October 2014, after struggling to break into the premier Hawthorn team during the regular season, Hallahan was traded to the Gold Coast Football Club.