Fantasy football season is not simply an August-to-January endeavor. Monitoring free-agent moves in March and April can be keys to draft success, as a new home can suddenly turn a player into a fantasy stud.

Or, in the the case of the backs that changed teams this offseason, knock them down a peg.

In 2011, playing for a new team and in a new offense turned Darren Sporles into a fantasy star, and returned Willis McGahee to a starting fantasy running back. In 2010, as the Chargers' No. 3 back, Sproles finished 43rd among running backs in fantasy points, scoring 5.61 points per game. McGahee took a back seat to Ray Rice in Baltimore that season and was ranked 50th among backs, scoring 5.17 fantasy points per week.

Sproles became one of Drew Brees’ favorite targets in New Orleans and excelled in the spread offense in 2011, moving up to 10th among backs at a clip of 11.58 points per game. McGahee went from backup to starter when he joined Denver, and the Broncos’ rush-first attack helped owners who took McGahee, as he scored the 21st-most fantasy points for running backs (10.27 per game).

Several things determine a player’s desire to test free agency and subsequently what team to join. A better chance to win, more money and more playing time are often the top factors.

Here’s a look at five notable backs who changed teams this offseason, and how their fantasy value will be affected. (A full fantasy analysis of the wide receivers who changed teams can be found in the 2012 PFW Fantasy Football Guide).

(The 2012 fantasy player rankings used below are from Pat Fitzmaurice's preseason draft board.)

Bears RB Michael Bush

2011 fantasy RB ranking: 9 (11.66 points per game)
2012 preseason RB ranking: 43