Few rookie campaigns have been as predictable as Mack's 2017. Stuck behind Frank Gore on the depth chart while playing in an offense that didn't present much of a vertical threat without Andrew Luck under center, the fourth-round pick out of South Florida couldn't produce big numbers, but he showed flashes of his big-play ability with seven runs of 15 yards or more on only 93 carries. At 6-0, 210, Mack compensates for his thin frame with speed that appears better than his 4.5 40 time, along with ankle-breaking moves that routinely leave defenders grasping at air. It's also worth noting he played through a torn labrum in his shoulder most of 2017 - ultimately requiring offseason surgery - which could explain his reluctance to run through tackles or fully engage blitzing pass rushers. Returning veteran Robert Turbin figures to be limited to short-yardage work once he returns from a four-game suspension, and while the Colts drafted Nyheim Hines and Jordan Wilkins to compete for snaps, the former profiles as a pass-catching specialist and the latter looks like a lesser version of Mack. If Luck can return and force safeties out of the box, the second-year back has the talent to exploit the extra space. Mack faces another obstacle after straining a hamstring in the first week of the preseason, leaving his Week 1 availability in doubt.