plaidshirts is correct. To get a sort of back button focus functionality on the X-T1 you have to use manual focus.
I believe the X-T2 will have a better feature for this with it being functional in S and C modes as well.
Quote from Ronin Photo Review
"What I think is one of the best customization features of this camera is that you can program the shutter button to do as you desire. Exposure lock and focus can be enabled or disabled as your discretion. This mean the X-T2 can do back button focus like your Canikon!"
http://roninphoto.blogspot.com/2016/07/the-fujifilm-x-t2.html