I was takin a break from doin hmwk and started doin some research on this (since I'm a Brown owner), figured I'd post my thoughts.
For 6 games last year (Week 9-14) Addai and Rhodes were both splitting touches. Check this out:
Colts Backfield, Week 9-14
Who was worth a fantasy start?
Addai Only: 1 Game (Week 11)
Rhodes Only: 2 Games (Week 10 & 14)
None Worthy: 2 Games (Week 9 & 13)
Both Worthy: 1 Game (Week 12)
Deeper Breakdown of Touches (Attempts and Receptions):
Week 9: 19 to 5 in Addai's Favor, (None Worthy)
Week 10: 14 to 9 in Addai's Favor, (Rhodes Only)
Week 11: 26 to 13 in Addai's Favor, (Addai Only)
Week 12: 23 to 12 in Addais' Favor, (Both Worthy)
Week 13: 16 to 11 in Addai's favor, (None Worthy)
Week 14: 12 to 13 in Rhodes Favor, (Rhodes Only)
Just health and age considered, you'd have to guess that Addai will be the hot hand early while he's fresh and while Brown is learning. As the season goes on, more wear and tear for Addai and more learning and comfort level for Brown, which should result in increased touches for Brown. I'm in a 2rb/3wr/3flex league, and Brown is on my bench. I don't expect him to be starting on my team much, not unless Addai has an injury or is completely ineffective (which I'm banking on as the year unfolds). Fact is the Colts are loyal to Addai. But this loyalty won't really disappear until BOTH of these things happen. 1) The Playoffs get closer and they feel pressure (to win, or to not lose), and 2). If Brown clearly gives Colts a better chance to win than Addai.
Another disturbing fact, the Colts running game isn't fantasy predictable. Take CJ and Lendale White. It's CJ's ball for 90 yards from the 5 to the 5. It's Lendale's ball for those other 10 yards of the field. Add to Lendale's touches the short yardage, some spelling here and there, and a heavier workload if they are leading in the 4th, and you pretty much know what to expect with the Titans run game fantasy wise. CJ will get you tons of yardage and receptions, hopefully a TD or two every other game, and Lendale will be a TD threat every game, hopefully sneak some good yardage in a game here or there.
Not nearly that easy for the Colts. If anyone watched Colts games last year, forget the Oline or whatever else excuse we have for a bad year by the running backs. If you add their stats you get about 1000 yards rushing and about 500 receiving and 16 TDs. If the workload wasn't perfectly split we'd be more looking at 1 fantasy stud with about 800 Rushing, 50 receptions, 300 Receiving, maybe 10-12 TDs which is very respectable.
But what really matters is how the Colts use their RB rotation. Last year they'd rotate the RBs by offensive POSSESSION, which isn't nearly as predictable as the Titans, who rotate by field position and situation. Colts would take turns 1 possession on 1 possession off, sometimes two on and two off. As the game went on, and the possessions got longer, they'd start rotating by SERIES. 4-8 Downs for Addai, 4-8 Downs for Rhodes.
Translation, unlike the Titans, the Colts running game will be guesswork all year until one of them gets injured. Not sure if this philosophy about RB rotation will carry through from last year though cuz of their coaching changes.
