Tonight at 10:00 p.m. ET on HBO the third episode of Hard Knocks, an annual five-episode documentary of an NFL training camp will air. This year's season will follow the Houston Texans, and can be live streamed free by clicking this link. Here are the three positional battlesto watch for during this episode as the Texans' training camp continues, and roster decisions become more concrete.

Check Out The Trailer For Tonight's Episode

Starting Running Back

Pro Bowler Arian Foster’s injury did not happen on camera, and so far there hasn’t been a ton of focus on who will replace him. Texans coach Bill O’Brien gave a big speech in the first episode about how the team needs to rally and make up for Foster’s absence rather than make excuses. That’s easier said than done.

Alfred Blue: Blue is the leader of the pack. He took over for Foster last season for a brief stretch, but didn’t play too well. He averaged a weak 3.1 yards per carry, partially exposing the offensive line as a middling unit that benefitted from Foster’s play.

Chris Polk: Polk’s case is hurt by having never started a game in his three-year NFL career. He does have a nose for the end zone, however. Polk has scored seven touchdowns despite only registering 57 career carries in his time with the Eagles. He is only slightly older than Blue, and has a good chance to sneak in front of this race with a good preseason performance or two.

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Jonathan Grimes: Grimes, 25, has already played on four teams and hasn’t really done much for any of them. He has averaged 3.7 yards per carry and scored one career touchdown. He is currently listed No. 2 on the depth chart behind Blue, but that’s due to familiarity. Expect Polk to rise up to at least No. 2, if not surpassing Blue at the top.

No. 2 Wide Receiver

Nate Washington: Washington is the elder statesman in this race. He hasn’t been particularly good the past couple of years, but coaches can count on the 31-year-old for baseline production in the 45-60 catch range with 1,000 yard being the absolute ceiling. That isn’t fantastic, but if DeAndre Hopkins becomes a legitimate star they won’t need much more.

Cecil Shorts III: Shorts was a target hound in Jacksonville, so he was a consistent sleeper for fantasy owners. In real life, he was the Jags’ de facto No. 1 and he did an okay job when he wasn’t hurt. It’s hard to imagine a wide receiver leaving Jacksonville but not improving his quarterback situation; Shorts is a rare breed indeed. Shorts is a 27-year-old version of Washington.

Jaelen Strong: This is who the Texans want to win the job, but the second episode had a segment dedicated to Strong’s battle with his own hands. Mental mistakes are plaguing the rookie receiver, and coaches are talking about it. With solid vets like Washington and Shorts in the fold, nothing will be handed to Strong. He’s tall and fast, so all he has to do is start hanging on to the rock.

Jadeveon Clowney vs. His Knee

This isn’t a positional battle, but it’s important. J.J. Watt is unquestionably the best defensive player in the NFL, but if Clowney, the No. 1 pick in 2014, reaches his potential, this could be the top defense in the NFL. Hard Knocks spent some time with him last week, and hopefully this episode will feature some more of his progress.

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