Elliott on 1st down
2016 5.5 ypc
2017 2.8 ypc
Elliott on 1st and 2nd down
2016 5.3 ypc
2017 3.4 ypc
The above stats are mine, from Pro Football Reference. The next two are from Adam Spinks@TheRBScout. In this first one, he determines the point (relative to the LOS) at which a defender is in tackling position. The players on the left have had the most running room. On the right are the players who have gained the most yards after this point.
In this next one, Spinks counts box defenders, but rather than simply listing those times when there was a certain number (8 in the box, for example), he takes offensive personnel into account and only lists those times when there was an
extra defender in the box relative to the number of blockers. According to Spinks, on 62% of Elliott's runs in the first four games, Dallas had at least as many blockers as there were box defenders.