''As we go into games, as games unfold, different things happen,'' Arians said this week, ''but the plan won't change.''
Although he has 51 fewer carries than Mendenhall, Ellington is the team's leading rusher with 388 yards in 54 attempts, an average of 7.2 yards per carry. Mendenhall, who has been bothered by a toe injury much of the season, has 323 yards in 105 carries for an average of 3.1 yards per attempt.
Ellington has an 80-yard touchdown run; Mendenhall's long gain for the season is 12 yards. But there's also the issue of what fans don't tend to see, such as pass blocking and veteran leadership.
Still, fans, radio talk show hosts and newspaper columnists have zeroed in on Mendenhall of late.
''That's fine,'' Arians said. ''Rashard can handle it; I can handle it.''
Mendenhall, in his sixth NFL season, said the criticism doesn't bother him.
''I've been around for so long, I've been through so much stuff, that's not really my focus,'' he said after Thursday's practice. ''I kind of keep things on the outside on the outside and focus on my work and my business and improving in that.''
Arians was offensive coordinator for four of Mendenhall's five seasons with the Pittsburgh Steelers. When Arians came to Arizona this season and the roster was overhauled, the Cardinals signed the free agent Mendenhall to a one-year contract.
Most of his runs have come on the inside, where yards have been hard to come by. Ellington, a sixth-round draft pick from Clemson who didn't have a carry in the season opener, has the speed to take things outside. In his 80-yard touchdown run two games ago against Atlanta, Ellington bounced to the outside and then raced to the end zone.
Arians has said that Ellington, at 5-foot-9 and 199 pounds, doesn't have the body to take the pounding of an every-down back. Ellington, though, said he could handle more carries.
''Of course, man,'' he said. ''It comes with the week of preparation and practice. If I carry the load in the game, I'll be fine.''
He shrugs off suggestions that he's not big enough for a larger work load.
''That's their opinion,'' Ellington said. ''I made it this far being the size that I am, why can't I go further? I don't have that doubt in my mind. My mentality is to go out there and be effective in everything I do.''
Arizona's best running game came against Atlanta, when Mendenhall was out with his toe problem.
The team rushed for 201 yards with Ellington getting 154 of them on a season-high 15 carries. Another rookie, Stepfan Taylor, took over Mendenhall's power back role and gained 38 yards in 14 attempts.
Ellington has had more rushing yards than Mendenhall in four of the last five games in which both have played, despite fewer attempts. Ellington also has 24 catches for 216 yards, Mendenhall 11 for 75 yards.
Offensive coordinator Harold Goodwin noted that, counting the pre-season, Ellington has played the equivalent of a full college season. But Ellington said he is far from worn out.
''Not at all, man,'' he said. '''I feel like they take pretty good care of us out there on the practice field so that when we get to the game we are ready to play.''
Asked what fans may not know about Mendenhall, Arians pointed to what happens during the week leading up to games.
''They don't sit in the room with those younger players,'' Arians said. ''If you really want to know what Rashard is giving the room, ask (running backs coach) Stump (Mitchell). Having been a veteran player in that room, he knows what that brings.''
In last Sunday's 27-24 victory over Houston, Mendenhall had 42 yards in 13 carries, including some crucial runs in the second half.
''To be real, I feel like I've been playing really well week in and week out,'' he said. ''Visually, there was a little more out there run-wise. We did a good job blocking. It was visually clear it was a better game. But me, I continue to build clearly to build on what I've been doing all year.''
Against the Texans, Mendenhall fumbled the ball away late at Arizona's 5-yard line. It was a play that Arians thought should have been blown dead long before J.J. Watt stripped the ball from Mendenhall's hands.
Arians said there's plenty of room for both running backs.
''The number of carries, a lot depends on how the flow of the game is going,'' he said. ''If one of them gets the hot hand, you're going to ride him a bit more.''
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