While he wasn't Matt Gillett circa 2010 as far as bolters go, Tautau Moga was certainly the Broncos biggest bolter of 2017. When he signed with the club, many saw him as a depth option and thought he'd only play a few games here and there. Instead he impressed on club debut and after some dicey moments, proved a real workhorse down that left hand edge. The club made the right decision letting him go to Newcastle, but his tenure wasn't as bad as fans make out.
The Broncos didn't play the Cowboys in the 2017 finals series. Were you thinking of the Melbourne Storm prelim where he blew an overlap out-wide? Or did he do something in the Round 2 clash against the Cowboys?