Carrying the ball into the heart of a defense, blocking to protect the quarterback and catching the occasional pass out of the backfield are the chores at hand for Stepfan Taylor, Jonathan Dwyer, Robert Hughes and Jalen Parmele.
The ability to play special teams helps, too, and will go a long way toward determining which of the backs are in uniform on Sundays.
''Pass protection and pounding the ball,'' coach Bruce Arians said. ''That's the role that we're looking for for a number of guys.''
Ellington, with speed and extreme maneuverability, is the starter, replacing Rashard Mendenhall, who retired. But Ellington is at his best in the open field, and he probably won't get many runs up the middle as the Cardinals try to ease the wear and tear on their prize second-year back.
Taylor and Dwyer appear to be the most probable to join Ellington as the top three backs.
''I feel like we could be a three-headed monster,'' Dwyer said.
The versatile Hughes also is forging a spot on the roster, as a running back, fullback and on special teams. And Parmele has had a strong training camp.
''Our running back room is probably the most talented group I've been a part of,'' Dwyer said. ''We're the youngest I've been a part of, so I'm very excited for our future.''
Arians expects to keep four, maybe five, running backs on the 53-man roster.
Of the four potential backups, Taylor is the only one with the team from last season.
Taylor was drafted in the fifth round out of Stanford, a round before Ellington was selected.
But Ellington emerged as a dynamic, big-play threat and Taylor toiled in the rugged space between the tackles, when he could get on the field.
''We control what we control,'' Taylor said. ''We do what the coaches put us in a position to do.''
Taylor played in all 16 games as a rookie, gaining 115 yards in 36 attempts, an average of 3.2 yards per carry. He also caught eight passes for 71 yards.
Dwyer came to Arizona after four seasons with Pittsburgh, the first two when Arians was the offensive coordinator. He prides himself on his pass protection.
''I feel like I'm one of the best that's out there,'' he said. ''I don't give up too many sacks. I've probably given up one in my career. I take a lot of pride in it, because the quarterback in this league is your team.''
Dwyer's best season was 2012, when he started six games and rushed for 623 yards in 156 attempts - an average of four yards per carry - and caught 18 passes for 106 yards. Last season, he had 49 carries for 197 yards, also an average of four yards per attempt.
Arians has had Ellington learn all of the receiver positions.
''He could start on a team as a wide receiver,'' the coach said, ''so you want to be able to use that skill and still have another back in the game that can do everything else.''
Arians' system usually doesn't have any fullback sets. But that's changed with the addition of Hughes, a 5-foot-11, 235-pound bowling ball of a player. Hughes has spent most of his first two seasons on the Indianapolis practice squad, appearing in five games in 2012 and one in 2013. In 2012, Arians was first the offensive coordinator, then the interim head coach of the Colts. Hughes, Arians said, is ''an outstanding tough guy.''
Hughes also gladly will play on special teams.
''In this league, it's all about the more you can do for a team,'' he said. ''I kind of pride myself in doing more than just one thing, being more than just a one-trick pony.''
Parmele, the only one of the five over 25, is trying to get back in the league after being out of football last season. He played in 16 games for Baltimore in 2010 and 11 for Jacksonville, two as a starter, in 2012. The other backs on the seven-deep depth chart are rookies Zach Bauman - from Northern Arizona - and Damien Thigpen - from UCLA.
NOTES: OG Jonathan Cooper, OT Nate Potter and TE Jake Ballard missed Tuesday's practice with sore knees. ... Rookie WR John Brown practiced after missing two days of workouts with a sore hamstring.
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