The word "fightin" is a shorter way of saying "fighting." It means engaging in physical or verbal combat or trying hard to achieve something despite difficulties. Full definition
An unlikely source of fightin» words began the skirmish when Lee Westwood said last week that assistant U.S. captain Tiger Woods could have an «adverse effect» on the team. (sbnation.com)
But it is more precious than ever and we must keep fightin for it. (politics.co.uk)
its great thanks but now me and one and three year old are fighting over fightin over the last few bites (mattbites.com)