It can be a bit dangerous to look at Murray last year and assume his success was all due to the OL.
Murray averaged more per carry in 2011 (5.5) and 2013 (5.2) with much less talented Dallas OLs than he did last year (4.7).
If the OL was the primary contributor to Murray's success, why did his ypc decline vs earlier in his career?
I sure hope your not suggesting his average is coming down because of the offensive line?
It's funny how you ask that question but the running game is more effective than ever before.
First, Murray's 2011 5.5 average is inflated because of the Ram's game. The Rams were the worst in run defense and at tackling that year. Or just remove the one 91 yard run in that game and his average is now 4.6. By the way, Murray did not even come within a hundred yards of that game for the rest of the year.
I also see you left out Murray's 2012 season when he averaged 4.1
But to answer your question on why is his average is coming down from earlier in his career. Is it because of the number of rushing attempts which has increased and will wear a running back down. Or is it because of play calling? Or a combination of both.
It is so much easier to run when your play calling is predominantly passing and your opponent is game planning for that.
Here are the Murray years in play calling;
2011 - Pass 58.3 / Run 41.7
2012 - Pass 64.9 / Run 35.1
2013 - Pass 63.5 / Run 36.5
2014 - Pass 48.3 / Run 51.7
Now let's look at the 2014 year. The Cowboys ran 52% of the time.
You knew it, I knew it and the opponents knew it. The Cowboys faced more 8-man fronts than any other team did last but they still gave Murray 850 yards before being touched! That was the most yards ever since they have started calculating that stat!
Yah it's the offensive lines fault Murray's average has come down.