Big chunk run plays require 2 things. 1. the OL needs to open a hole for the RB to get to the 2nd level, or capture the edge to allow the RB to get outside. 2. Blocking at the 2nd level. The Cowboys are getting neither. Their receivers cannot block downfield and their TEs cannot hold their blocks.
I think the Lions were doing a lot of run blitzing, shooting guys into the run gaps and hitting Pollard behind the LOS. At least that's how it looked on TV. But then when the Cowboys would pitch the ball outside they were shooting past blockers and hitting Pollard before he could turn upfield. The Lions play the run really well and you can see how quickly they pursue and gang tackle. Pollard still got off a couple of good runs on them, just not enough.
