Colts Mailbag: What's RB depth chart look like after Frank Gore?

Let's dive into this week's version of the Indianapolis Colts mailbag.

Mike Wells: Frank Gore is obviously the starter and Daniel Herron is his backup with Zurlon Tipton and Josh Robinson competing for the third running back spot. Vick Ballard, who is trying to work his way back from a torn ACL and Achilles the past two seasons, had a setback earlier this week when he suffered a hamstring injury in practice. Ballard's not only trying to overcome the physical hurdle of being injured the past two seasons, he's also trying to get over the mental obstacle of it too, because the past two seasons have been brutal for him. He has to get back to simply playing football and not thinking about his knee, Achilles and now his hamstring when he gets back on the field. Wells: Find some wood and knock on it because the Colts have used the same starting five up front -- Anthony Castonzo, Lance Louis, Khaled Holmes, Todd Herremans and Jack Mewhort -- in every practice in training camp so far. The talk on offense rightfully centers around Andrew Luck and his playmakers at running back, tight end and receiver, but the Colts' offensive success this season will be determined by how well the offensive line blocks. Protect Luck and open holes for running back Frank Gore and the Colts will be one of the best offensive teams in the league. Do a poor job in both of those areas and it'll be a challenge for the Colts to reach their ultimate goal of winning a Super Bowl. Wells: The battle for the No. 3 receiver is wide open. The primary candidates for that position are Donte Moncrief, who is currently getting most of the snaps at that position, Phillip Dorsett and Duron Carter. All three have made their cases for that spot at different points in training camp so far. Carter was the Colts' best receiver in practice Friday. He had four touchdown receptions in practices. It wouldn't be surprising if the Colts gave him more snaps with the second and maybe even the first unit in practice to see how well he does going against some of their better cornerbacks. Sit back and enjoy watching the battle for the No. 3 receiver spot because it's going to be a fun one.