A club attempting to remove a player from the 40-man roster and send him to the Minor Leagues must first place that player on outright waivers, allowing the 29 other Major League clubs the opportunity to claim him. The claiming club assumes responsibility for the remaining money owed to the claimed player, who is placed on his new club's 40-man roster. Should the player clear waivers, he can be sent to any Minor League affiliate the club chooses. Outright waivers are also used when clubs wish to remove a player who is out of Minor League options from the 25-man roster by sending him to the Minors.
If a player has more than three years of Major League service time or was previously outrighted in his career (by his current club or another club), he is eligible to reject the outright assignment and instead opt for free agency. Players with more than three but less than five years of Major League service time must forfeit any remaining guaranteed money on their contract if they reject an outright assignment. Conversely, those with five or more years of Major League service time are still owed any guaranteed money remaining on their contract, should they elect free agency following an outright.
When the Red Sox removed Allen Craig from their 40-man roster on May 18, 2015, he was still guaranteed approximately $25.2 million. That was likely one of the reasons he went unclaimed on waivers, allowing Boston to outright him to the Minors. Given his standing as a player with more than three but less than five years of service time, Craig would have had to forfeit the remaining money on his contract in order to test free agency. Thus, he accepted an assignment to Triple-A.