The Colorado Rockies have been using a four-man pitching rotation since mid-June, and the plan was to continue that through the 2013 season. However, something has changed for Colorado as Tony Renck of the Denver Post is reporting that the Rockies will go to a five-man rotation with three piggy back pitchers, and a higher pitch count from 75 to closer to 100.
The theory seems to be the same as with a four-man rotation by having piggy back or hybrid pitchers who are able to start or be a long reliever. It's not clear what triggered the change, because the four-man set up has improved the team's ERA from 6.28 to 5.61.
By going back to a league-standard five-man rotation, it seems that the Rockies felt that the four-man rotation experiment was not a success..