In Tomb Raider (2018), Rog and Bill discussing about fox hunting i.e i.e person is supposed to carry a fox tail on the back of her bike while a team of bikers chase after them :
Rog: Got 30 hounds signed up. Just gotta find a fox now.
Bill: Tough one, that. Need someone quick enough to make it interesting.
Rog: Yeah. No fun if they ain't quick.
Why is "that" placed at the end of the sentence? Why can't written as that is tough one?