Mahaffey becomes the second fullback signed in the last two weeks, following former Texas A&M scoring machine Jorvorskie Lane.
To stay at the 90-player roster limit after the signing of Ochocinco, the Dolphins released center Terence Brown. Let go to make room for Mahaffey was former Penn State wide receiver Derek Moye, like Brown an undrafted rookie free agent.
The 90-man roster limit remains in effect until Aug. 28, at which time teams must get down to 75 players. Three days later, following the last preseason game, teams must set their 53-man roster.